Visual Studio 2022 problem after upgrade to last version 17.2.6

This issue is caused not by the Visual Studio update from 17.2.5 to 17.2.6, but by the update from .NET SDK 6.0.301 to 6.0.302 (which is automatically done during the Visual Studio upgrade). Intellisense is still looking for the code analyzers in the old SDK directories.

To find this, you should actually not look at the errors, but at the warnings (seeing you have 56 warning, I guess you tend not to look at them. It's a very good habit to keep the number of warnings at 0). Inbetween the warnings you should see something like:

Warning CS8034 Unable to load Analyzer assembly C:\Program Files\dotnet\sdk\6.0.301\Sdks\Microsoft.NET.Sdk\analyzers\Microsoft.CodeAnalysis.CSharp.NetAnalyzers.dll: Could not find a part of the path ‘C:\Program Files\dotnet\sdk\6.0.301\Sdks\Microsoft.NET.Sdk\analyzers\Microsoft.CodeAnalysis.CSharp.NetAnalyzers.dll’.

How I fixed it: by manually opening the properties (alt-enter) of each problematic project. If you do that, it automatically fixes the paths.

Hans Passant's fix (deleting all the obj directories) seems way simpler, and might be a good thing to do on any Visual Studio upgrade. (Note, only delete the build obj directories, not those of dependencies, like git/github/node-modules/etc)

edit: Note that there is a side-issue with .NET SDK 6.0.302, where source generators run twice, which breaks anything that relies on them, like the WPF- and WinUI community toolits.

edit2: Microsoft has notified that these issues should be solved with the next release/update.