The referenced component 'System' could not be found. (or any other component for that matter)

Question

Issue: Just started today, all references to any assembly outside of the solution fail to resolve, with The referenced component 'SomeComponent' could not be found. when trying to build. This happens for both 3rd party components (all 15 or so of them) as well as all .NET Framework assemblies - basically anything that isn't another project in the same solution.

Trying to load some other solutions produced the same issue. Creating a new WinForms project worked without a problem, however. (Scratch that, it worked before reinstalling VS, now that doesn't work either. I created a new WinForms app as well as a WPF app, and the designer can't load the assemblies either. I tried targetting 3.5 and 2.0 and no luck.)

Things I've tried:

• Repair Visual Studio installation
• Rebooting computer
• Started VS with /resetsettings flag
• System Restore to 2 days ago when it was known to be working
• Uninstalling VS and reinstalling
• Fresh checkout from SVN

Does anyone have any experience with this and know of a way to get this working again? My strongest Google-fu has failed me, so I'm asking here. Can mark community wiki if requested.

Update: I tried "upgrading" Windows (to the same version) since I didn't see a repair option for Vista and it's still a no-go. I reinstalled everything that seemed relevant. So far, it's looking like I'm just gonna have to back up and reformat I guess unless a solution comes up sometime before tomorrow.

Update2: I just backed up data and reformatted, so I'm no longer able to verify any ideas that I haven't tried yet, so I'll just leave the bounty to expire on its own to the top voted answer and as a reference to anyone else who may have this problem later.

Answer 1

I had the same problem. It turns out that something was wrong with NuGet. I removed the following part of the *.csproj-File (opened in a text editor). This has solved the issue for me:

<Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
    <PropertyGroup>
        <ErrorText>This project references NuGet package(s) that are missing on this computer. Enable NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
    </PropertyGroup>
    <Error Condition="!Exists('$(SolutionDir)\.nuget\NuGet.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\.nuget\NuGet.targets'))" />
</Target>

Answer 2

In my case, the solution was completely different. It looked like it was an issue with NuGet paths (caused by my moving the project to a different solution and then back again.

I edited the .csproj and removed all references to NuGet and associated packages. I also removed the packages folder from the solution folder.

The system components then magically reappeared.

Answer 3

Suggested next debug step: review Project Designer: References -> Reference Paths to verify that the paths to your system and third-party components appear correctly. (Watch out for things that can slip past the old Mark I Eyeball like drive letters.)