I'm adding this here because it caused me a headache this morning while fixing our build server:
Executing dotnet build
would show me the following errors:
DOTNET1011: Framework not installed: .NETFramework,Version=v4.6.1
error NU1001: The dependency mscorlib could not be resolved.
The error is confusing, as I DO have the .NETFramework,Version=v4.6.1 installed.