The project system has encountered an error When trying to load project

I found that you need to do two steps to resolve this issue:

1. Delete the .vs folder at the solution level.
2. Delete the bin and obj folders in all projects within the solution.

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I encountered the issue in Visual Studio 2017 v15.7.4 and the affected project/solution was created in v15.7.4, so it can occur without upgrading to a new version of Visual Studio.

Try deleting bin and obj folders in all projects of that solution.

Probably those folders were having old files generated by some older version of visual studio, which are not compatible with new version of visual studio.