Answer by Anrijs Vītoliņš for Could not find a part of the path ... bin\roslyn\csc.exe

If you were adding ASPNETCOMPILER to compile your Razor views in MVC, like in this StackOverflow question, then change PhysicalPath to place where Roslyn nuget package is located (usually pointed via $CscToolPath variable):

<Target Name="AfterBuild" Condition="'$(MvcBuildViews)'=='true'"><AspNetCompiler VirtualPath="temp" PhysicalPath="$(CscToolPath)" />