Predefined type 'System.Object' is not defined or imported .net 4.6

Question

I\'m using MVC 5 and .net 4.6 to create a web API that my mobile app can connect too.

Whenever I build the project I get hundreds of errors telling me that I need to add

Answer 1

Took almost 2 days to fix. Tried VS Uninstall\re-install several times but did not work.

What finally worked for me...

Ran VS Installer repair. Due to errors, I had to manually uninstall all instances MS .NET Core SDK - 2.1xxx

Ran VS Installer repair. No errors. Remove bin and obj and rebuild.

Ran dotnet restore command on Package manager console and problem solved.