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c#,shared folder,windows server [duplicate]

I'm trying to read an Excel (xlsx) file using the code shown below. I get an "External table is not in the expected format." error unless I have the file already open in Excel. In other words, I have to open the file in Excel first before I can read if from my C# program. The xlsx file is on a share on our network. How can I read the file without having to open it first?
Thanks
string sql = "SELECT * FROM [Sheet1$]";
string excelConnection = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + pathname + ";Extended Properties=\"Excel 8.0;HDR=YES;IMEX=1;\"";
using (OleDbDataAdapter adaptor = new OleDbDataAdapter(sql, excelConnection)) {
DataSet ds = new DataSet();
adaptor.Fill(ds);
}

"External table is not in the expected format." typically occurs when trying to use an Excel 2007 file with a connection string that uses: Microsoft.Jet.OLEDB.4.0 and Extended Properties=Excel 8.0
Using the following connection string seems to fix most problems.
public static string path = #"C:\src\RedirectApplication\RedirectApplication\301s.xlsx";
public static string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";

Thanks for this code :) I really appreciate it. Works for me.
public static string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";
So if you have diff version of Excel file, get the file name, if its extension is .xlsx, use this:
Private Const connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";
and if it is .xls, use:
Private Const connstring As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & "Data Source=" + path + ";Extended Properties=""Excel 8.0;HDR=YES;"""

(I have too low reputation to comment, but this is comment on JoshCaba's entry, using the Ace-engine instead of Jet for Excel 2007)
If you don't have Ace installed/registered on your machine, you can get it at: https://www.microsoft.com/en-US/download/details.aspx?id=13255
It applies for Excel 2010 as well.

Just add my case. My xls file was created by a data export function from a website, the file extention is xls, it can be normally opened by MS Excel 2003. But both Microsoft.Jet.OLEDB.4.0 and Microsoft.ACE.OLEDB.12.0 got an "External table is not in the expected format" exception.
Finally, the problem is, just as the exception said, "it's not in the expected format". Though it's extention name is xls, but when I open it with a text editor, it is actually a well-formed html file, all data are in a <table>, each <tr> is a row and each <td> is a cell. Then I think I can parse it in a html way.

I had the same problem. which as resolved using these steps:
1.) Click File
2.) Select "save as"
3.) Click on drop down (Save as type)
4.) Select Excel 97-2003 Workbook
5.) Click on Save button

I had this same issue(Using the ACE.OLEDB) and what resolved it for me was this link:
http://support.microsoft.com/kb/2459087
The gist of it is that installing multiple office versions and various office sdk's, assemblies, etc. had led to the ACEOleDB.dll reference in the registry pointing to the OFFICE12 folder instead of OFFICE14 in
C:\Program Files\Common Files\Microsoft Shared\OFFICE14\ACEOLEDB.DLL
From the link:
Alternatively, you can modify the registry key changing the dll path to match that of your Access version.
Access 2007 should use OFFICE12, Access 2010 - OFFICE14 and Access
2013 - OFFICE15
(OS: 64bit Office: 64bit) or (OS: 32bit Office: 32bit)
Key: HKCR\CLSID{3BE786A0-0366-4F5C-9434-25CF162E475E}\InprocServer32\
Value Name: (Default)
Value Data: C:\Program Files\Common Files\Microsoft
Shared\OFFICE14\ACEOLEDB.DLL
(OS: 64bit Office: 32bit)
Key:
HKCR\Wow6432Node\CLSID{3BE786A0-0366-4F5C-9434-25CF162E475E}\InprocServer32\
Value Name: (Default)
Value Data: C:\Program Files (x86)\Common Files\Microsoft
Shared\OFFICE14\ACEOLEDB.DLL

I have also seen this error when trying to use complex INDIRECT() formulas on the sheet that is being imported. I noticed this because this was the only difference between two workbooks where one was importing and the other wasn't. Both were 2007+ .XLSX files, and the 12.0 engine was installed.
I confirmed this was the issue by:
Making a copy of the file (still had the issue, so it wasn't some save-as difference)
Selecting all cells in the sheet with the Indirect formulas
Pasting as Values only
and the error disappeared.

I was getting errors with third party and Oledb reading of a XLSX workbook.
The issue appears to be a hidden worksheet that causes a error. Unhiding the worksheet enabled the workbook to import.

If the file is read-only, just remove it and it should work again.

I know this is a very old post, but I can give my contribution too, on how I managed to resolve this issue.
I also use "Microsoft.ACE.OLEDB.12.0" as a Provider.
When my code tried to read the XLSX file, it received the error "External table is not in the expected format."
However, when I kept the file open in Excel and then the code tried to read it ... it worked.
SOLUTION:
I use Office 365 with company documents and in my case, the solution was very simple, I just needed to disable the sensitivity of the document, setting it to "public".
Detail: Even after saving as "public" the green check still remained marked in "Internal Use", but the problem remained solved after that.

I had this problem and changing Extended Properties to HTML Import fixed it as per this post by Marcus Miris:
strCon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & importedFilePathAndName _
& ";Extended Properties=""HTML Import;HDR=No;IMEX=1"";"

ACE has Superceded JET
Ace Supports all Previous versions of Office
This Code works well!
OleDbConnection MyConnection;
DataSet DtSet;
OleDbDataAdapter MyCommand;
MyConnection = new System.Data.OleDb.OleDbConnection(#"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=..\\Book.xlsx;Extended Properties=Excel 12.0;");
MyCommand = new System.Data.OleDb.OleDbDataAdapter("select * from [Sheet1$]", MyConnection);
DtSet = new System.Data.DataSet();
MyCommand.Fill(DtSet);
dataGridView1.DataSource = DtSet.Tables[0];
MyConnection.Close();

Ran into the same issue and found this thread. None of the suggestions above helped except for #Smith's comment to the accepted answer on Apr 17 '13.
The background of my issue is close enough to #zhiyazw's - basically trying to set an exported Excel file (SSRS in my case) as the data source in the dtsx package. All I did, after some tinkering around, was renaming the worksheet. It doesn't have to be lowercase as #Smith has suggested.
I suppose ACE OLEDB expects the Excel file to follow a certain XML structure but somehow Reporting Services is not aware of that.

the file might be locked by another process, you need to copy it then load it as it says in this post

This can also be a file that contains images or charts, see this: http://kb.tableausoftware.com/articles/knowledgebase/resolving-error-external-table-is-not-in-expected-format
The recommendation is to save as Excel 2003

Just adding my solution to this issue. I was uploading a .xlsx file to the webserver, then reading from it and bulk inserting to SQL Server. Was getting this same error message, tried all the suggested answers but none worked. Eventually I saved the file as excel 97-2003 (.xls) which worked... only issue I have now is that the original file had 110,000+ rows.

If you still have this problem, then check your permissions, I tried many of these suggestions and my concrete problem was that the file that I wanted to process was under source control and the thread had no permissions, I had to change the entire folder permissions and it started to work (I was processing many files in there)... It also matches many suggestions like change the name of the file or check that the file is not loicked by another process.
I hope it helps you.

Instead of OleDb, you could use the Excel Interop and open the worksheet as read-only.
https://msdn.microsoft.com/en-us/library/microsoft.office.interop.excel.workbooks.open(v=office.15).aspx

This can occur when the workbook is password-protected. There are some workarounds to remove this protection but most of the examples you'll find online are outdated. Either way, the simple solution is to unprotect the workbook manually, otherwise use something like OpenXML to remove the protection programmatically.

I recently saw this error in a context that didn't match any of the previously listed answers. It turned out to be a conflict with AutoVer. Workaround: temporarily disable AutoVer.

That excel file address may have an incorrect extension. You can change the extension from xls to xlsx or vice versa and try again.

I recently had this "System.Data.OleDb.OleDbException (0x80004005): External table is not in the expected format." error occur. I was relying on Microsoft Access 2010 Runtime. Prior to the update that was automatically installed on my server on December 12th 2018 my C# code ran fine using Microsoft.ACE.OLEDB.12.0 provider. After the update from December 12th 2018 was installed I started to get the “External table is not in the expected format" in my log file.
I ditched the Microsoft Access 2010 Runtime and installed the Microsoft Access 2013 Runtime and my C# code started to work again with no "System.Data.OleDb.OleDbException (0x80004005): External table is not in the expected format." errors.
2013 version that fixed this error for me
https://www.microsoft.com/en-us/download/confirmation.aspx?id=39358
2010 version that worked for me prior to the update that was automatically installed on my server on December 12th.
https://www.microsoft.com/en-us/download/confirmation.aspx?id=10910
https://www.microsoft.com/en-us/download/confirmation.aspx?id=10910
I also had this error occur last month in an automated process. The C# code ran fine when I ran it debugging. I found that the service account running the code also needed permissions to the C:\Windows\Temp folder.

Working with some older code and came across this same generic exception. Very hard to track down the issue, so I thought I'd add here in case it helps someone else.
In my case, there was code elsewhere in the project that was opening a StreamReader on the Excel file before the OleDbConnection tried to Open the file (this was done in a base class).
So basically I just needed to call Close() on the StreamReader object first, then I could open the OleDb Connection successfully. It had nothing to do with the Excel file itself, or with the OleDbConnection string (which is naturally where I was looking at first).

I've had this occur on a IIS website that I host, rarely but periodically this error will popup for files that I've previously parsed just fine. Simply restarting the applicable app pool seems to resolve the issue. Not quite sure why though...

This happened to us just recently. A customer of ours was getting this error when trying to upload their excel file on our website. I could open the xlsx file fine on ms excel and don't see any irregularities with the file. I've tried all mentioned solutions in here and none worked. And i found this link Treating data as text using Microsoft.ACE.OLEDB.12.0. What worked for our case is adding IMEX=1 attribute to the connection string. So if you are using Microsoft ACE OLEDB 12.0 this might help fix your issue. Hope this helps.
<add name="ExcelTextConnection" connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 12.0;HDR={1};IMEX=1'" />

Import Excel 2013 to vs, Microsoft ACE.OLEDB.12.0 is not registered on the local Machine

Creating a form application in vs 2012. I have office 2013 installed, win 8 64 bit. I get the above error for the below piece of code.
public void SetConnection(string text1, string text2, string text3, string text4, string text5, string text6, string text7)
{
connectionString1 = "Initial Catalog=test; Data Source=work\\sqlexpress";
connectionString = "Data Source='c:\\Users\\test1.xlsx';Extended Properties=Excel 12.0 Xml;Readonly=False;";
database = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;" + connectionString);
database.Open();
database1 = new OleDbConnection("Provider=SQLOLEDB.1;" + connectionString1);
database1.Open();
}
I tried using jet drivers but would not work, so i turned to ace. First i got "Cannot find installable ISAM"; so installed AccessDatabaseEngine_x64 which leads me to this error. I then changed my build to x86 and same errors. So i'm out of options. I did try previous versions of AccessDatabaseEngine from 2007 and 2010 but no luck, any suggestions.

database = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source='c:\\Users\\test.xls';Extended Properties= \"Excel 8.0;HDR=Yes;IMEX=1\";");
The above connection string works using jet although i have to leave the excel file open for the time being as i get "could not decrypt file" error otherwise. I also had to save the file as a 97-03 excel xls file.

string connectionString = "Provider=Microsoft.Jet.OleDb.4.0;Extended Properties=Excel 12.0 Xml;HDR=YES; Data Source=C:\Users\q\Desktop\Ug\Test.xlsx";

As said here, probably you have the 64-bit office installed which doesn't have the 32-bit compnents installed (links are provided there). You may also have to biuld your project targetint x86 platform.

Sharepoint 2010 with excel 2010 error

This is the first question for me on this site, and I wish my issue will be solved by you :)
I am creating a small utility which reads from a SharePoint List and from Excel sheet in order to map fields for doing some kind of migrating data from excel to SP list,
The utility is first populating SP lists from SharePoint depending on the URL provided, then loads columns for the selected List in a Datagrid, then it reads excel sheet and populates all columns in another datagrid:
the first problem I faced was that I was not able to add Microsoft.Sharepoint.dll this was solved by changing .Net Framework from .NET Framework 4 Client Profile to .NET Framework 3.5 since I got the below error:
Error 1 The type or namespace name 'SharePoint' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
So Far SharePoint is working fine, Now when attempting to read from Excel sheet, I get error the below Error:
I have used OLEDB and ODBC connections as below, but none worked under x64:
string sConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + this.textBox3.Text + ";Extended Properties='Excel 8.0;HDR=Yes;IMEX=1'";
The 'Microsoft.Jet.OLEDB.4.0' provider is not registered on the local machine.
string sConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + this.textBox3.Text + ";Extended Properties=Excel 12.0;";
The 'Microsoft.ACE.OLEDB.12.0' provider is not registered on the local machine.
string sConnectionString = "Driver={Microsoft Excel Driver (*.xls, *.xlsx, *.xlsm, *.xlsb)};DBQ="+ this.textBox3.Text +"";
ERROR [IM002] [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified
After some search, I read that we need to build this application under 86x to solve excels issue, I did that and the problem was solved for excel, but now SharePoint is not working and giving the error message below:
The Web application at
http://localhost/ITO could not be
found. Verify that you have typed the
URL correctly. If the URL should be
serving existing content, the system
administrator may need to add a new
request URL mapping to the intended
application.
As you see, Excel Columns are populated here, but SharePoint is giving error!!
Any Idea in how to let both of them work in the same application??

Microsoft.SharePoint.dll is only for Applications running on the SharePoint server, not for Apps running on a client machine. For Client Applications, use the Client Object Model or the Web Services.
When using the SharePoint DLLs, the Application must be x64, not x86 (the default for Console Apps) or AnyCPU - SharePoint 2010 is 64-Bit only. (The above Client OM works on 32-Bit of course)
When using the SharePoint DLLs, use .net 3.5, but you already figured that out :)
Technically, using Microsoft.SharePoint.dll outside of SharePoint (either the website or a timer job) isn't supported either - it works in most cases though.

I would start by saying that Sharepoint 2010 need to be run in 64bit and on .net 3.5. Get that sorted, and your sharepoint will work. You might then have to install 64bit version of excel to get it working on the same platform.
WHat you have now is a hotch potch of 3.5 and 4.0, and 64 bit and 32 bit parts, which will never work together.

I have installed MS office for 64 bits and that solved my issue :)

How do I connect to different versions of Excel from C#?

I have a program that imports data from Excel into a dataset. To connect to Excel I use the following code...
return new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" +
fileName + "; Jet OLEDB:Engine Type=5;"+ "Extended Properties=\"Excel 8.0;\"");
I just got a new computer with Excel 2010 and now the connection attempt fails and throws an exception saying The 'Microsoft.Jet.OLEDB.4.0' provider is not registered on the local machine
Is this because the new version of Excel needs a different connection string? Has anyone run into this?
EDIT:
Actually I just read somewhere that using the System.Data.OleDbClient class does not require Excel to even be installed on the computer. So my problem probably has nothing to do with Excel but rather with the Microsoft.Jet tool. My computer is running Windows7 64 bit. Shouldn't that be installed already?

Check out the Microsoft Access Database Engine 2010 Redistributable.
Redistributables for other Excel versions also exist.

You need to compile your program specifically for 32-bit so it will run in the WoW subsystem and invoke the 32-bit Jet provider. As mentioned above, there is no 64-bit version of the Jet provider and likely never will be.
In Visual Studio, you do this by setting your target CPU type in the project settings to x86 instead of Any or 64-bit.
If you don't have the source for your program, you can modify the .exe using the corflags.exe utility that comes with the .NET framework and the /32bit+ flag, but if it's a strongly signed assembly you'll need the .SNK to re-sign it once you've modified it.
Here is a reference on WoW64 if you need more detail: http://en.wikipedia.org/wiki/WoW64

I find this site useful when having connection string questions.
http://www.connectionstrings.com/excel
Also take a look at a previous SO question:
Diagnosing an OLEDB exception when Quering Excel 2010

Excel "External table is not in the expected format."

I'm trying to read an Excel (xlsx) file using the code shown below. I get an "External table is not in the expected format." error unless I have the file already open in Excel. In other words, I have to open the file in Excel first before I can read if from my C# program. The xlsx file is on a share on our network. How can I read the file without having to open it first?
Thanks
string sql = "SELECT * FROM [Sheet1$]";
string excelConnection = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + pathname + ";Extended Properties=\"Excel 8.0;HDR=YES;IMEX=1;\"";
using (OleDbDataAdapter adaptor = new OleDbDataAdapter(sql, excelConnection)) {
DataSet ds = new DataSet();
adaptor.Fill(ds);
}

"External table is not in the expected format." typically occurs when trying to use an Excel 2007 file with a connection string that uses: Microsoft.Jet.OLEDB.4.0 and Extended Properties=Excel 8.0
Using the following connection string seems to fix most problems.
public static string path = #"C:\src\RedirectApplication\RedirectApplication\301s.xlsx";
public static string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";

Thanks for this code :) I really appreciate it. Works for me.
public static string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";
So if you have diff version of Excel file, get the file name, if its extension is .xlsx, use this:
Private Const connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";
and if it is .xls, use:
Private Const connstring As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & "Data Source=" + path + ";Extended Properties=""Excel 8.0;HDR=YES;"""

(I have too low reputation to comment, but this is comment on JoshCaba's entry, using the Ace-engine instead of Jet for Excel 2007)
If you don't have Ace installed/registered on your machine, you can get it at: https://www.microsoft.com/en-US/download/details.aspx?id=13255
It applies for Excel 2010 as well.

Just add my case. My xls file was created by a data export function from a website, the file extention is xls, it can be normally opened by MS Excel 2003. But both Microsoft.Jet.OLEDB.4.0 and Microsoft.ACE.OLEDB.12.0 got an "External table is not in the expected format" exception.
Finally, the problem is, just as the exception said, "it's not in the expected format". Though it's extention name is xls, but when I open it with a text editor, it is actually a well-formed html file, all data are in a <table>, each <tr> is a row and each <td> is a cell. Then I think I can parse it in a html way.

I had the same problem. which as resolved using these steps:
1.) Click File
2.) Select "save as"
3.) Click on drop down (Save as type)
4.) Select Excel 97-2003 Workbook
5.) Click on Save button

I had this same issue(Using the ACE.OLEDB) and what resolved it for me was this link:
http://support.microsoft.com/kb/2459087
The gist of it is that installing multiple office versions and various office sdk's, assemblies, etc. had led to the ACEOleDB.dll reference in the registry pointing to the OFFICE12 folder instead of OFFICE14 in
C:\Program Files\Common Files\Microsoft Shared\OFFICE14\ACEOLEDB.DLL
From the link:
Alternatively, you can modify the registry key changing the dll path to match that of your Access version.
Access 2007 should use OFFICE12, Access 2010 - OFFICE14 and Access
2013 - OFFICE15
(OS: 64bit Office: 64bit) or (OS: 32bit Office: 32bit)
Key: HKCR\CLSID{3BE786A0-0366-4F5C-9434-25CF162E475E}\InprocServer32\
Value Name: (Default)
Value Data: C:\Program Files\Common Files\Microsoft
Shared\OFFICE14\ACEOLEDB.DLL
(OS: 64bit Office: 32bit)
Key:
HKCR\Wow6432Node\CLSID{3BE786A0-0366-4F5C-9434-25CF162E475E}\InprocServer32\
Value Name: (Default)
Value Data: C:\Program Files (x86)\Common Files\Microsoft
Shared\OFFICE14\ACEOLEDB.DLL

I have also seen this error when trying to use complex INDIRECT() formulas on the sheet that is being imported. I noticed this because this was the only difference between two workbooks where one was importing and the other wasn't. Both were 2007+ .XLSX files, and the 12.0 engine was installed.
I confirmed this was the issue by:
Making a copy of the file (still had the issue, so it wasn't some save-as difference)
Selecting all cells in the sheet with the Indirect formulas
Pasting as Values only
and the error disappeared.

I was getting errors with third party and Oledb reading of a XLSX workbook.
The issue appears to be a hidden worksheet that causes a error. Unhiding the worksheet enabled the workbook to import.

If the file is read-only, just remove it and it should work again.

I know this is a very old post, but I can give my contribution too, on how I managed to resolve this issue.
I also use "Microsoft.ACE.OLEDB.12.0" as a Provider.
When my code tried to read the XLSX file, it received the error "External table is not in the expected format."
However, when I kept the file open in Excel and then the code tried to read it ... it worked.
SOLUTION:
I use Office 365 with company documents and in my case, the solution was very simple, I just needed to disable the sensitivity of the document, setting it to "public".
Detail: Even after saving as "public" the green check still remained marked in "Internal Use", but the problem remained solved after that.

I had this problem and changing Extended Properties to HTML Import fixed it as per this post by Marcus Miris:
strCon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & importedFilePathAndName _
& ";Extended Properties=""HTML Import;HDR=No;IMEX=1"";"

ACE has Superceded JET
Ace Supports all Previous versions of Office
This Code works well!
OleDbConnection MyConnection;
DataSet DtSet;
OleDbDataAdapter MyCommand;
MyConnection = new System.Data.OleDb.OleDbConnection(#"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=..\\Book.xlsx;Extended Properties=Excel 12.0;");
MyCommand = new System.Data.OleDb.OleDbDataAdapter("select * from [Sheet1$]", MyConnection);
DtSet = new System.Data.DataSet();
MyCommand.Fill(DtSet);
dataGridView1.DataSource = DtSet.Tables[0];
MyConnection.Close();

Ran into the same issue and found this thread. None of the suggestions above helped except for #Smith's comment to the accepted answer on Apr 17 '13.
The background of my issue is close enough to #zhiyazw's - basically trying to set an exported Excel file (SSRS in my case) as the data source in the dtsx package. All I did, after some tinkering around, was renaming the worksheet. It doesn't have to be lowercase as #Smith has suggested.
I suppose ACE OLEDB expects the Excel file to follow a certain XML structure but somehow Reporting Services is not aware of that.

the file might be locked by another process, you need to copy it then load it as it says in this post

This can also be a file that contains images or charts, see this: http://kb.tableausoftware.com/articles/knowledgebase/resolving-error-external-table-is-not-in-expected-format
The recommendation is to save as Excel 2003

Just adding my solution to this issue. I was uploading a .xlsx file to the webserver, then reading from it and bulk inserting to SQL Server. Was getting this same error message, tried all the suggested answers but none worked. Eventually I saved the file as excel 97-2003 (.xls) which worked... only issue I have now is that the original file had 110,000+ rows.

If you still have this problem, then check your permissions, I tried many of these suggestions and my concrete problem was that the file that I wanted to process was under source control and the thread had no permissions, I had to change the entire folder permissions and it started to work (I was processing many files in there)... It also matches many suggestions like change the name of the file or check that the file is not loicked by another process.
I hope it helps you.

Instead of OleDb, you could use the Excel Interop and open the worksheet as read-only.
https://msdn.microsoft.com/en-us/library/microsoft.office.interop.excel.workbooks.open(v=office.15).aspx

This can occur when the workbook is password-protected. There are some workarounds to remove this protection but most of the examples you'll find online are outdated. Either way, the simple solution is to unprotect the workbook manually, otherwise use something like OpenXML to remove the protection programmatically.

I recently saw this error in a context that didn't match any of the previously listed answers. It turned out to be a conflict with AutoVer. Workaround: temporarily disable AutoVer.

That excel file address may have an incorrect extension. You can change the extension from xls to xlsx or vice versa and try again.

I recently had this "System.Data.OleDb.OleDbException (0x80004005): External table is not in the expected format." error occur. I was relying on Microsoft Access 2010 Runtime. Prior to the update that was automatically installed on my server on December 12th 2018 my C# code ran fine using Microsoft.ACE.OLEDB.12.0 provider. After the update from December 12th 2018 was installed I started to get the “External table is not in the expected format" in my log file.
I ditched the Microsoft Access 2010 Runtime and installed the Microsoft Access 2013 Runtime and my C# code started to work again with no "System.Data.OleDb.OleDbException (0x80004005): External table is not in the expected format." errors.
2013 version that fixed this error for me
https://www.microsoft.com/en-us/download/confirmation.aspx?id=39358
2010 version that worked for me prior to the update that was automatically installed on my server on December 12th.
https://www.microsoft.com/en-us/download/confirmation.aspx?id=10910
https://www.microsoft.com/en-us/download/confirmation.aspx?id=10910
I also had this error occur last month in an automated process. The C# code ran fine when I ran it debugging. I found that the service account running the code also needed permissions to the C:\Windows\Temp folder.

Working with some older code and came across this same generic exception. Very hard to track down the issue, so I thought I'd add here in case it helps someone else.
In my case, there was code elsewhere in the project that was opening a StreamReader on the Excel file before the OleDbConnection tried to Open the file (this was done in a base class).
So basically I just needed to call Close() on the StreamReader object first, then I could open the OleDb Connection successfully. It had nothing to do with the Excel file itself, or with the OleDbConnection string (which is naturally where I was looking at first).

I've had this occur on a IIS website that I host, rarely but periodically this error will popup for files that I've previously parsed just fine. Simply restarting the applicable app pool seems to resolve the issue. Not quite sure why though...

This happened to us just recently. A customer of ours was getting this error when trying to upload their excel file on our website. I could open the xlsx file fine on ms excel and don't see any irregularities with the file. I've tried all mentioned solutions in here and none worked. And i found this link Treating data as text using Microsoft.ACE.OLEDB.12.0. What worked for our case is adding IMEX=1 attribute to the connection string. So if you are using Microsoft ACE OLEDB 12.0 this might help fix your issue. Hope this helps.
<add name="ExcelTextConnection" connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 12.0;HDR={1};IMEX=1'" />