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C# DataSet Namespace

So I've seen similar questions asked regarding this but none of the answers ever solved my issue. So I'm going to ask for myself.
I have a web application written in C# with VS2010. The website runs perfect uncompiled. When I attempt to build the application, I get a lot of errors like: "The type or namespace name 'XXXXTableAdapter' could not be found (are you missing a using directive or an assembly reference?"
The pages are coded as: 'using XXXXTableAdapter;' which always shows an error in the intellisense.
The dataset XSD files have the Build Actions set to 'None' with the custom tool 'MSDataSetGenerator'. The file 'XXXXTableAdapter.Designer.cs' starts with 'namespace '{APP}.App_Code {'
I read that you should be able to prefix the using XXXXTableAdapter; like using {APP}.App_Code.XXXXTableAdapter but I can never get this to work.
I think I'm missing some code somewhere so I can access the tableadapters from any page using the application namespace.
Any ideas?

To change/adjust/fix the namespace of the datasets, you need to:
Highlight the DataSet's XSD file in the solution explorer
Open the property window
Change the "Custom Tool Namespace" value to whatever you want the namespace to be (say, your application namespace)
I've noticed it will default the namespace of the dataset to the directory structure your file is in, which is kind of annoying unless your code structure explicitly follows your directory structure.

You should refrences to all the dll's that you are accessing to your project, since it is not possible to tell which dll you are missing, you should find them yourself from errors and add them, also after that add their namespace to your class. That will resolve all the issues.

The type or namespace name 'ConfigurationManager' does not exist in the 'NamespaceA.NamespaceB' (are you missing an assembly reference?)

For missing namespace, I added a reference to relevant project which contains the namespace.
Code detected the reference and go stable
I then compiled the code.
Again, I am getting the same error and the code became like this
Please help ! I have no clue what is going on. This ConfigurationManager is being used since ages in our solution (which has many projects). I have created a project in the solution and there is where I am getting this error
I tried these, but didn't help
Type or Namespace Error
C# web project complaining about a class
The type or namespace name 'X' does not exist in the namespace 'Y' - in VS generated code

For this issue you have to add ConfigurationManager namespace to your project.
ConfigurationManager is part of System.Configuration in .NET. You should add a reference to your project if you want to use ConfigurationManager after .NET 2.0. As you mentioned you're using .NET 4.0 so you must add a reference to the System.Configuration dll.
Then you should try using System.Configuration.ConfigurationManager.
Update : If you have custom made class so you probably made a mistake while making or using the class.
Read this article may help you.
Hope it helps

Compilation errors in Reference.cs after adding a Service Reference caused by multi-part namespace

I hit this weird namespace issue when adding my first 'Service Reference' to a client project in Visual Studio 2010.
If my project's default namespace uses two or more parts, e.g. MyCompany.MyApp then when adding a Service Reference a Reference.cs file is created containing the namespace MyCompany.MyApp.ServiceReferenceName with a lot of auto-gen code with fully qualified names, e.g. System.SerializableAttribute, System.Runtime.Serialization.DataContractAttribute.
The Reference.cs file will be full of compilation errors because the compiler starts treating the System namespace as sub member of the MyCompany.MyApp namespace. You get an awful lot of errors along the lines of:
The type or namespace name 'Runtime' does not exist in the namespace 'MyCompany.MyApp.System'...
If I amend the namespace at the top of the Reference.cs file to something simple, e.g. MyCompanyMyApp.ServiceRefernceName then the compiler behaves and recognises the System namespace references as decleration of .net's System namespace.
I'm using a different workaround for now as I really want to keep my multi-part namespaces. My current alternative is to append global:: in front of the System namespace references to force the complier to do the right thing. In fact, if the 'Add Service Reference' wizard uses T4 templates I may just amend those to embed my workaround at the source.
Questions
I'd really like to understand what's going on here and why a multi-part namespace causes this issue. Presumably there's more to namespaces than I thought. Secondly, would really like to work out a better solution than performing a global Find/Replace every time I add a Service Reference or mucking around with some T4 templates.

I found the answer here somewhat unclear, so I thought I would add this as an example (I would do it in the comments but it looks better here):
So I have this as my default namespace:
namespace RelatedData.Loader
But I also add a class named:
public class RelatedData
{
}
Because the class name matches a portion of the namespace when it generates your proxy with Add Service Reference it gets confused.
The answer here was to rename my class:
public class RelatedDataItem

Ahh well I found the cause eventually.
I'm working against a very large third party WCF API and ... one of their namespaces is LameCompany.System (!!) Carnage then ensues...
Arrrgghhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
The lesson to learn here is when Visual Studio/.net compiler stops recognising the BCL's System namespace you have a namespace/type in your project called System. Find it, remove it, shoot the developer that created it.

I found that having a class name similar to your namespace causes this.
Try renaming your class name

I ran into a similar issue with VS2012 described by jabu.hlong and Simon Needham after minor changes in the client project that has the references to the WCF services after updating the reference to the services. I got lots of errors compiling the Reference.cs files generated and so on (the generated files of the XAML as well).
I have selected to reuse types from specific assemblies in my solution and got a similar problems with the namespaces.
The error I get is that the namespace of the reused assembly and the namespace of the generated types can not be found when used in the Reference.cs. Both namespaces have in common the first parts, as they are from the same solution. My namespaces in the solution are like appname.tier.technology.project. Both conflicting namespaces are Appname.Dto.Modulename (the reused assembly) and Appname.Client.Wpf.ServiceName (the namespace in the client project using the services for the generated types).
The problem arises after a minor change in the client project, when I created a new utility class in the namespace Appname.Client.Wpf.Appname. I choose that namespace because the Appname is also the name of a module in the client project. This seems to confuse the compiler and can not resolve both namespaces in the generated Reference.cs. After changing the namespace of the utility class to avoid using two identical parts in it and updating the service reference, the compiler errors in Reference.cs dissapears.

I tried different things (and tried different namespaces when adding the service reference), but nothing worked for me except this brute force fix - in my case it was OK but I am aware it's ugly (and needs to be repeated if you use "Update Reference" in the future):
Since the WCF service namespace is added to your default namespace, just search and replace all mentions of the newly added
MyNamespace.ServiceNamespace
with
ServiceNamespace
in the whole solution (use your own namespaces of course), including the auto-generated Reference.cs file.

Basically, the problem is a name conflict where one name is hiding another. A folder or class named "System" can do that, but if you also have a class with the same name as your project, you'll see the same thing. Sure, you can rename everything in the reference.cs, but it's probably better to rename your conflicting class.

I had folder in my project called "System" (yes, very stupid of me) and that caused some issues in the references.cs.
Renaming the folder (and the namespace), fixed the issue.

Here is how I solve this issue on VisualStudio 2017 trying to add a reference to a web service in a test project.
After trying adding the references, rebuilding, closing, reopening and spending some time on the issue, I noticed that VS had put the files it creates to reference the WS in a folder named "Connected Services".
I renamed the folder without the space then opened all the files in the folder and the csproj with a text editor, replaced all the occurrences of "Connected Services" to "ConnectedServices" and reopened the project.
I then added references to System.Runtime.Serialization and System.ServiceModel and everything now works fine.

This is a bug in Visual Studio (still is at version 2022). To fix, remove the namespace in the reference.cs file. So if your namespace is "myapplication" and your service is "myservice", you'll see myapplication.myservice in the reference.cs file. just delete "myapplication." everywhere and make sure it isn't auto-generated again (lest you have to re-delete everything).

Compile error: 'The type or namespace name 'Runtime' does not exist in the namespace 'MyAppNamespace.System' (are you missing an assembly reference?)'

I am writing a WPF client that consumes services from an ASP web service (VS2010, .net 4.0). It was working just fine until yesterday when I suddenly get the above compiler error. Double-clicking on the error takes me to Reference.cs and highlights just about anything along the lines of:
[System.Runtime.Serialization.DataMemberAttribute(EmitDefaultValue=false, Order=2)]
(The 'Runtime' object is highlighted as not being in the MyAppNameSpace).
I've tried googling this and re-adding the service reference and re-adding the assemby reference but nothing works and I'm completely stuck. Reference.cs is automatically generated and I'm still relatively new to VS2010 so I'm not sure where to go with this.
Hoping someone here can point me in the right direction...?

I had the same problem. After hours of trying to solve it I realised I had a class in my library called system. What a cock.

Your problem is that you had defined a "System" namespace somewhere that the compiler and Intellisense were finding before the real "System". The solution is to remove the offending namespace, then clean and rebuild the project.

I had the same issue with a VB project only I had no old code as it was a new service reference. I did not have any other namespace with System in the name. The solution for me was to make the following series of replacements:
VB
in Reference.vb
Replace System. with nothing
Then replace "Runtime.Serialization" with "System.Runtime.Serialization"
Lastly replace <Global.ComponentModel with <ComponentModel
C#
in Reference.cs (I didn't try this but expect it will work)
Replace System. with nothing
Then replace "Runtime.Serialization" with "System.Runtime.Serialization"
Lastly replace [Global.ComponentModel with [ComponentModel
One other detail that might lead someone to a root cause is that the service wsdl was coming from an old style asp.net web service (.asmx), here: https://api.mindbodyonline.com/0_5/ClassService.asmx?wsdl
Update
I've subsequently found that changing the target framework to 4.5.1 resolved my compilation issue. Also I had the root cause was that I had different framework versions targeted by my web project and the class library containing my service references. Once I changed them all to 4.5.1 everything was happy no changes to Reference.vb was needed.

Well, for the sake of anyone looking for an answer in future - I gave up trying to fix it and copied a backup of the project files over the existing ones and brought the changes since them in manually. That fixed the corrupt referencing issue.

I had a similar problem, but with a different solution.
My project used to be called "JobRunner", but it changed to "NGB.JobRunner". In the project settings however the default namespace and assembly name was still "JobRunner", and the Reference.cs file was being generated with this namespace.
I have no idea why it was causing problems, but when I fixed the default project namespace and assembly name, and re-added the service reference, problem solved!

I had the similar problem. It was the upper case 'T' in time which was causing the issue. I was doing RunTime but the correct was 'Runtime'.
What a time waste due to a typo!!

App_Code folder issues

So I'm having a really weird issue with my App_Code folder on a new website I'm designing.
I have a basic class inside of a namespace in the App_Code folder. Everything works fine in the IDE when I setup the namespace and make an object from the class. It brings up the class summary on hover, and when you click on "go to deffinition" it goes to the class file.
And it also works fine localy.
However, when I load the site onto my server, I get this error message when I access that page:
Line 10: using System.Web.UI.WebControls;
Line 11: using System.Web.UI.WebControls.WebParts;
Line 12: using xxxx.xxxx
Compiler Error Message: CS0246: The type or namespace name 'xxxxxx' could not be found (are you missing a using directive or an assembly reference?)
I know for a fact that the class file is there. Anyone have any idea of whats going on?
Edits:
John, yes it is a 2.0 site.

The problem that your classes are not compiled, You'll solve this issue simply by going to the properties of any class in the App_Code folder and change it's 'Build Action' property from "Content" to "Compile"

If your application is a Web Application project rather than a Web Site project, the code files should not be in the App_Code folder (stupid design, I know). Create a new folder called code or something and put them in there.
It caused me all sorts of problems when I upgraded a bunch of old .Net web sites to application projects.

This just happened to me and the solution was that App_Code (and App_Data) were not put in the root of the server, but in a subfolder that held everything else. Must be in root!

I have noticed a mismatch sometimes between the IDE parser and the compiler whenever a compile-time error occurs in a referenced assembly or code file. In that circumstance the IDE will correctly identify the types and provide full support for them, but since the compiler was unable to create the referenced objects, it will complain that the referenced objects don't exist.
Now I don't want to go accusing anybody of anything—this is just a guess—but you should probably make sure there are not any errors in your referenced code file.

Depending on how you publish the site, it won't look in App_Code, it'll look for a DLL in the Bin folder that contains the class instead. How did you transfer your website to the server?

For those that follow...I had this same set of issues but it was caused because I named a class in App_Code, 'HTML'. Took a long while to figure out that it was just a name conflict because the compiler wasn't being very helpful about telling me what the problem was.