Getting an Unexpected Call

I'm working with the Autodesk COM Interop library and am getting this error:

TypeMock.TypeMockException :
*** Unexpected Call to Inventor.DrawingDocument.get_DisplayName()

The InventorDrawingDocument doesn't show as available for me to set up an Isolate.WhenCalled on it.

The error gets thrown when mockDrawing.DisplayName is accessed.

Any thoughts on how to set that up so that I don't get this problem?