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Visual Studio stopped supporting my projects

I have Visual Studio 2013 Ultimate. Today when I opened it, it didn't load any of my solution's projects. Error message:
Unsupported
This version of Visual Studio is unable to open the following projects. The project types may not be installed or this version of Visual Studio may not support them.
For more information on enabling these project types or otherwise migrating your assets, please see the details in the "Migration Report" displayed after clicking OK.
- ETL_<Project name>, "<Project path></Project>.csproj"
Non-functional changes required
Visual Studio will automatically make non-functional changes to the following projects in order to enable them to open in Visual Studio 2013, Visual Studio 2012, and Visual Studio 2010 SP1. Project behavior will not be impacted.
- <Project name></Project>, "<Project path></Project>.sln"
These projects are of types Class Library and Console Application. If I try to create a new project, these types are listed, but when I create it I get message <Project path> cannot be opened because its project type (.csproj is not supported by this version of the application. To open it, please use a version that supports this type of project..
So, Visual Studio is telling me it doesn't support a project it just created?! GJ M$!!

Unfortunately I was unable to solve this. I ended up uninstalling VS Ultimate. Now I use VS Express for Desktop, and it works with my old projects.
My assumption is that something on Windows broke some part of VS. I should have tried to uninstall and reinstall it but didn't have the opportunity.

I have the same thing in a Hyper-V VM. After repair did not work, I deinstalled and reinstalled VS 2017. Same thing.
In the host I can still open the same project with VS, so it is not the project, but the VS install that has a problem.
It puts this in the migration log:
src\DTOWEB\project.json: Failed to migrate XProj project DTOWEB. Could not find project.json at C:\DTOWeb\DTOWEB7\src\DTOWEB\project.json.
I have a second VM that is x86 iso x64, and it can open the project without problems. So again, my conclusion is there is nothing wrong with the project.

Downgrading solution from Visual Studio 2017 RC to Visual Studio 2015

I have had a project in VS 2015 Update 3 with a lot of code logic behind. I upgraded it to VS 2017 RC successfully. The code implementation went on and on until getting to the point where VS 2017 RC exhibited a lot of issues and instabilities e.g. .Net Core DLL template removed! by installer or Resource file could not be compiled and so forth! I'd like to revert the solution back to VS 2015 to keep working flawlessly but it's impossible easily due to a lot of code implemented in VS 2017 excluding new Roslyn features. Any suggestions how to perform the downgrade?

You will also need to update your *.vcxproj files, to change the toolset referenced there to the one used by the earlier compiler.
What I found useful, is to create a small scratch project (just simple console app) in each version of visual studio, then use beyond compare or similar to contrast the .sln and .vcxproj files from each vs version. This will show you the toolset changes and maybe a few others that you need. For example going from vs 2017 to vs 2019 the toolset changes from 141 to 142.
So the lines
<PlatformToolset>v141</PlatformToolset> are for vs2017
and
<PlatformToolset>v142</PlatformToolset> is for vs2019

It's indeed a manual process and no there are no tools that can automate that.

I had the same problem and i fixed it using this solution:
1) create a solution of whichever project you want (winforms, etc)
2) browse to your project folder and find your .sln file.
3) open it using notepad.
4) copy the first 4 lines as shown
here.
5) find your .sln file for the project you wish to downgrade. for example : foo.sln (its found where your project is).
6) open it with notepad and paste the lines instead of the first 4 lines
7) save and open the sln. it should open it under visual studio 2015
i hope this works for you

This project(Visual Studio 2012 express) is incompatible with the current version of Visual Studio 2013 express

Am doing a back end project in C# in Visual Studio. My team mate had done it using Visual Studio 2012 express and everything seems to work there. But when i used git to clone it to my system where am using Visual Studio 2013 express, one part of the project says its incompatible with the current version of VS. I could clean and build the project, but was unable to run the project. I searched and found that one solution is to go to Programs and features, select VS, right click,select repair. But even after doing this, the problem persists. Is there any work around?

When I was learning ASP.NET MVC by Informit tutorials I was in the very similar situation. I downloaded the sample sources that was created in VS2013 but had VS2015 installed. It was some kind of bug \ magic, but VS didn't recognized some libraries in VS2015 even they were installed. What is more strange is the fact that when I decided to totally rewrite the project line by line it worked!
Of course, I tried to clean, rebuild, reinstall NuGet packages.
So, if you have an access to sources *.cs, then just try to create new project and copy-paste code.

Visual studio doesn't support specific csproj file

I am getting this error when I try to open the solution file of my project. The solution is 2012 file (checked using notepad).
If I click on Ok, The solution opens up except for one csproject which does not load.
I get a migration report in UpgradeLog.htm file, with the following error for the project which failed to load. Could not figure out much from it.
Error:
The application which this project type is based on was not found.
Please try this link for further information:
http://go.microsoft.com/fwlink/?prd=12395&pver=11&sbp=ProjectTypeDeprecated&plcid=0x409&clcid=0x409&ar=MSDN&sar=ProjectCompatibility&o1=82b43b9b-a64c-4715-b499-d71e9ca2bd60
Does the upgrade report mean that it is a project from previous version of Visual studio? It does not open in Visual Studio 2010 either.

The error doesn't say that Visual Studio doesn't support .csproj files at all, it says it doesn't support a specific project type in that particular project file. This means this either isn't your project as you claim, or you are trying to build it on a different machine from the one used to create the project.
Visual Studio uses various elements in a .csproj file to determine its project type. See How do you tell the Visual Studio project type from an existing Visual Studio project and What is the significance of ProjectTypeGuids tag in the visual studio project file. It does this so it knows how to compile your project, what properties tabs to show, what context menu options should be available and so on.
Certain project types can cause this error. Usually they require some kind of SDK to be installed on the machine used to open or build the project.
You should search the web for the GUID mentioned in the error message you show (the value after o1=). You can also open the project file in a text editor and find the <ProjectTypeGuids> elements, which contains comma-separated project type GUIDs.
Then search the web for those GUIDs to find out which SDK or tool you need to install in order to be able to open or build the project.
If you paste the specific GUID from your error message in your favorite web search engine, you'll find Problem solved: Visual Studio / There is a missing project subtype. Subtype: '{82b43b9b-a64c-4715-b499-d71e9ca2bd60}' is unsupported by this installation., where it is mentioned you'll need to install the Visual Studio 2013 SDK. This means that in this case, your project is a Visual Studio 2013 extension.
This is what documentation is for. You should at least put a ReadMe.txt file in your project directory, explaining what the prerequisites for building a project are, especially when it won't open or build with Visual Studio out of the box.

I had this issue when I used Update 5 for VS 2013.
For me I had to click ok and read the next few steps, that popped up. I was initially clicking cancel.
On mine the project was missing Web Tools, so had to reinstall those and once done it was working.
Hope that helps someone.

This issue also appears when trying to import an ASP.Net project into Visual Studio 2015 Express for Desktop, and can be solved by simply downloading and installing Express 2015 for Web - or by using Visual Studio Community/Standard.

I am currently using VS 2017 v 15.7.4. This error came out of no where without any updates on my part. Usually when I have errors like this I just delete the .vs folder in my solution and that clears the problem. In this case that is what I did and the problem was fixed.
Close VS
Delete .vs folder
Load VS
Note: This was for a Xamarin based solution.

I solved this problem by downloading and installing (Microsoft Visual Studio Installer Projects). Close the project then install. After the installation, open your project then reload .csproj file

I had the same issue with VS 2017.
Eventually i solved it by just enable the SSIS in the following way:
1. In VS 2017 - Click on Extensions and Updates in the Tools menu.
Locate the Microsoft Integration Services Projects.
if you can't find it then you will have to install it first.
Click on the Enable button.
Close VS and start it again and SSIS projects are now available.
enter image description here

This (the error that states "Visual studio doesn't support specific csproj file") also occurs when the .vs folder is removed; however, closing and reopening Visual Studio will resolve the error.

Force project AND solution upgrade from VS2010 to VS2013, not just solution file [duplicate]

Trying to open a VS 2012 solution (SLN file) explicitly in VS 2013 succeeds. Simply double-clicking it in Windows Explorer still opens it in VS 2012 instead.
I've read "Visual Studio 2012 doesn't convert vs2010 solution?" and followed the suggestion to "Save As..." the solution file.
Still it opens in VS 2012 by default.
My question:
How to change a SLN file to force it being opened in Visual Studio 2013?

The .sln file indicates the intended version as one of the early lines - for example:
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2013
or:
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2012
However - it can only make use of this if the default application for .sln files is the "Microsoft Visual Studio Version Selector". It is not uncommon for the default .sln application to be a specific version instead. In windows 8:
you can tell which is the default because it says "keep using":

Note that you can also force the upgrade of a .sln or .proj file by using the commandline, where devenv is the target IDE version:
devenv "MyProject.sln" /upgrade
Example:
"%programfiles(x86)%\Microsoft Visual Studio 12.0\Common7\IDE\devenv.exe" "D:\Source\MySolution.sln" /upgrade
Note that this does not open Visual Studio. An alternative is to, from within the IDE, select "Save As" for your solution file and overwrite or save the solution under new name.
Read more:
http://msdn.microsoft.com/en-us/library/w15a82ay.aspx

Seems like the OP has a working answer already ... but for me the problem was different. I had a VS 2012 solution (several actually) and wanted to convert them to 2013 (which I understand is a trivial change to the .sln file, but I wanted it done automatically in case there was some secret upgrade logic I was unaware of).
So I thought I would open it in VS2013, it would automatically upgrade as expected, and then I'd be set to double click the solution and see it in VS2013 going forward. But opening in VS2013 was NOT upgrading the solution for me automatically as expected and I could not find an explicit way to force the upgrade after opening the file in VS2013. I could work with the solution, save my changes, and close VS2013, but the .sln would remain unchanged and un-upgraded.
Turns out my problem was in how I was opening the solution ... as a habit I right click files and select "open with" to choose the program I want to use to open a file. I do this frequently. Note I am NOT talking about changing the default "open with" program but just opening a file with a specific program once. So I would right click the .sln file... open with Visual Studio 2013 ... and nothing would upgrade.
Eventually I thought to go into VS2013, then do File > Open and select the .sln file (this is foreign to me since I hardly if ever open anything this way, maybe you are the same way). Anyway that did upgrade the solution file instantly.
After upgrading, lines 2-3 of the .sln file changed from this:
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2012
to this:
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2013
VisualStudioVersion = 12.0.30501.0
MinimumVisualStudioVersion = 10.0.40219.1
So from my experience, to automatically update a VS2012 .sln to VS2013, you must open VS2013 and select the .sln from the File > Open dialog. Using the explorer shell to force the .sln file to open in VS2013 does not invoke the upgrade logic (apparently).
As a further note, I tested with another solution, and after making changes through Configuration Manager (which obviously "touches" the .sln file) it did upgrade a VS2012 to VS2013, even after having opened it through right-click open with.

I had a solution that had previously been upgraded from 2010 to 2013 successfully but still showed the .sln as associated with 2010.
I tested all the methods given in this thread and the only one that successfully corrected the .sln was to open Visual Studio 2013 alone, then open the solution that still was associated with 2010 in the IDE, then use the [File] > [Save (name).sln as] to overwrite the existing .sln file.
Setting the file assoc of the .sln to be the "Visual Studio version selector" made no change and the solution continued to open in 2010.
The devenv (name).sln /upgrade method made no change to my .sln file.
Hacking the raw text of the .sln file corrupted mine and it would not open at all.

To solve this issue I just changed the following lines of the .sln file:
Microsoft Visual Studio Solution File, Format Version 11.00
# Visual Studio 2010
into these:
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2013
The comment line is to be changed as it is parsed by the solution loader.
Update:
A better approach is to use the devenv command line as pointed in another reply, which will do it safely for you.

This may work for readers attempting to upgrade a solution file to Visual Studio 2015. (I upgraded a VS 2012 solution.)
Open the solution in VS 2015.
Add a new project to the solution. (I added a test project.)
Remove the project.
Save the solution.
You may want to delete the removed project folder at this time since step 3 did not delete it.
This worked for me when neither zumey’s nor TCC’s answers did.
EDIT
Metro Smurf had a similar, but easier answer than mine for a similar question. His steps were:
Open solution in VS 2015
Right-click solution > Add > New Solution Folder (name does not matter)
Save solution
Delete the newly added solution folder
Save solution