Issue with cyclic Import statements

I've had a similar problem with a branching heirarchy where lower classes are duplicated, e.g.

A -> B -> C
A -> D -> C

Class A uses class B which uses class C
Class A also uses class D which also uses class C

When I used Include this produced the Duplicate Identity problem, however once I converted to Import it worked fine!

So make sure you try Import before you try the Abstract base class approach, it worked for me!