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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.

Open Visual Studio 2008 Solution in Visual Studio 2013 without Upgrading

In short: I need to open an application originally built in Visual Studio 2008 (version 9) in Visual Studio 2013 without upgrading the project since the overall project architecture must remain the same for when I check it back into source control.
Details: I need to open a Visual Studio solution (.sln) inside Visual Studio 2013. The solution in question was originally developed in Visual Studio 2008, so when I try to open said solution in Visual Studio 2013, I am shown a prompt with the projects within the solution checkmarked, with the message:
These projects are either or supported or need project behavior impacting modifications to open in this version of Visual Studio. Projects no displayed either require no changes or will automatically be modified such that behavior is not impacted. Visual Studio will automatically make functional changes to the following projects in order to open them. You will not be able to open these projects in the version of Visual Studio in which they were originally created.*
My attempt at a fix was to just upgrade the solution and hope for the best. This is successful, but after building and attempting to run the main project, I see the following build error:
The type 'Microsoft.Web.Services3.WebServicesClientProtocol' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.Web.Services3, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. *
I then tried both commenting out the references to this assembly and adding in the missing reference. Okay, so then I rebuilt the solution and attempted to run. Same error, but for a different assembly. Repeat fix, same error for different assembly. This pattern continues and continues, and at this point I realize this is unacceptable anyway, because when I make a change to this solution, I need to check it back into source control. When others open it, they may be opening it in VS2008, and therefore this “upgraded” version is inconsistent with the version the business uses. I need to open the solution originally build in VS2008 in VS 2013 (can't work around this, needs to be VS2013). If it helps, I'm using 64 bit Visual Studio 2013 Ultimate.
Any help or guidance will be greatly appreciated!

As several of the commenters have already helpfully pointed out, this is not possible. Round-tripping (i.e., opening and manipulating project files created by an older version of Visual Studio in a newer version of Visual Studio) was not supported until Visual Studio 11. The only way to open a Visual Studio 2008 project/solution in a later version of Visual Studio will be to convert it.
As far as interoperability with previous versions is concerned, you have two options:
Update the project locally (using the migration wizard provided), make any changes to the project file necessary to get it to build, and then edit the code files. Once you're satisfied with your edits, commit only the modified source files, not the project infrastructure files. Your fellow developers, stuck on VS 2008, won't notice any difference.
Update the project locally (using the migration wizard provided), make any changes to the project file necessary to get it to build, and then rename the project file (e.g., by appending a -vs2013 suffix to it). Commit this to your code repository. You will now have two project files in your root directory, one for each version of Visual Studio that your team works with. From here on, you just open the project file corresponding to the version of VS that you have installed.
I used approach #1 for a good part of last year, where I spent most of my time developing a C++ application in VS 2010 on a desktop machine, but also wanted to work on it on my notebook running VS 2013. Of course, in my case, it took a trivial amount of time for the automatic conversion to upgrade my project file after pulling from source control. I didn't have to do any tweaking thereafter to get the project to build. It sounds like your case is different, so option #2 might be a better choice.

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.

Bulid SQLite-Net Extensions in visual studio professional 2013 but not successful

I am new to windows app and I am going to build the sqlite-net extension project to .dll file in order to make the models have the relationship attribute of one-to-many, one-to-one, many-to-many.
Link: https://bitbucket.org/twincoders/sqlite-net-extensions
This is the info that it shows when I open the project in visual studio 2013.
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.
- IntegrationTests.Touch-MvvmCross, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\IntegrationTests.Touch\IntegrationTests.Touch-MvvmCross.csproj"
- IntegrationTests.Touch-PCL, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\IntegrationTests.Touch\IntegrationTests.Touch-PCL.csproj"
No changes required These projects can be opened in Visual Studio
2013, Visual Studio 2012, and Visual Studio 2010 SP1 without changing
them.
- Tests, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\Tests\Tests.csproj"
- MvvmCross, "MvvmCross"
- SQLiteNetExtensions-MvvmCross, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\SQLiteNetExtensions\SQLiteNetExtensions-MvvmCross.csproj"
- SQLiteNetExtensions-PCL, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\SQLiteNetExtensions\SQLiteNetExtensions-PCL.csproj"
- SQLiteNetExtensions, "C:\Users\**\Downloads\sqlite-net-extensions\sqlite-net-extensions\SQLiteNetExtensions.sln"
I try to build it and it shows some errors. So I right click the project and download the missing packages. When I try to build it again, it shows these errors:
Does anyone successfully bulid it to .dll file or anyone can fix the problems like these?
Many Thanks!

The Integration test projects are MonoTouch projects, that won't open in Visual Studio unless you have Xamarin Business license installed in your PC.
However, the SQLite-Net Extensions project is a standard PCL project and you will be able to compile it from Visual Studio without Xamarin. The problem that you are describing is probably related to not having the SQLite-Net dependency downloaded.
Make sure that you have NuGet Package Manager plugin installed and restore NuGet packages for the project to restore the dependencies and it should work.
You can also download the pre-compiled DLL from the Download page in the project page.

I solved it with changing the build platform. Thx guys!

VS 2010 SP1 - The project type is not supported by this installation

I have a visual studio 2010 Ultimate SP1 using a solution where two of my .csproj projects will not open. The error i get is the project type is not supported by this installation.
It's not a problem with the solution as these projects open with no issue on all other workstations.
My project type guid's are and seem to be the same for both projects that are unavailable within the solution:
{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}
{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}
I checked all of my prerequisites and they seem to be installed correctly. I noticed when opening up visual studio sometimes the license name is different. I'm wondering if there could be a conflict with a previous install? Any suggestions would be helpful.
Thanks.

It looks like your missing Portable Library tools. Are you sure it's installed?
If not, http://visualstudiogallery.msdn.microsoft.com/b0e0b5e9-e138-410b-ad10-00cb3caf4981

The reason of the issue is that you're trying to open a project where it's template is not installed in your VS 2010. For example by default VS2010 has no MVC3, MVC4, and Silverlight 5 templates. You need to install them if you want to open their project types.
To download MVC3 or MVC4 installers visit http://www.asp.net/mvc