I had to use mono 5.20.1 sucessfully with python 3.7 and pythonnet (please see this),

I started MonoDevelop and loaded QuantConnect.Lean successfully, but building gave 1 error:

Error MSB4019: The imported project                                                "/home/scubamut/.cache/MonoDevelop/7.0/MSBuild/15153_1//Microsoft.CSharp.Core.targets" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk. (MSB4019) (QuantConnect.Logging)

I know python but I don't know Mono or Visual Studio, so I need help to tell me how to resolve the problem.