Could not load file or assembly 'System.Security.Principal.Windows'

Question

Solution has compiled successfully, but after I added an existing class file to the project, this error appeared:

The specified task executable \"csc.exe\

Answer 1

I do not like removing packages without first understanding what I'm removing. I faced the same problem with my solution.

I discovered that 1 of the many projects was using the Microsoft.Net.Compilers NuGet package - let's call it Project ABC. A Unit Test project was referencing that Project ABC, but not the Microsoft.Net.Compilers NuGet package.

I simply referenced the Microsoft.Net.Compilers NuGet package from my Unit Test project, and the problem has now gone away.