We currently have a Winforms application targeting .NET Framework 4.

When trying to upgrade to 4.5.2 we get an error:

The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'

How do we go about the upgrade?

Any help would really be appreciated.