COM and MFC-Serialize

I just created my first ActiveX Project using the MFC ActiveX Control Wizard. In one method I want to deserialize an (structured) object. Doing so I get the exception from the Load method inside Serialize that one special class is unknown. This class is in an dll which is loaded.
When I create an MFC-Projekt doing the same thing everything is fine. Any hints what might be wrong or where the difference might be?

Thanx
Hans-Peter