DoExternalDrop override (please help)

How to override DoExternalDrop function using Visual C++.NET. I have try it, but there was an error message

error C3153: ‘Northwoods::Go::IGoCollection’ : you cannot create an instance of an interface".

I have to use Visual C++.NET to build my application (user requirement).

Does anybode have using GoDiagram.NET with Visual C++.NET?