VBA and DLL ActiveX

I have created an ActiveX DLL using Visual Basic 6.0.
It works good in a Visual Basic application! Not so good when I try to use it in a Visual Basic for Application code (MS Excel in this case): I cannot see the User Defined Types which I defined with the "Public Type......" clause in my component. Moreover VBA does not allow such a command:

Collection.Add Variable

where Variable is of a User Defined Type.
Deos anyone know what's wrong with VBA (or with my object)?

Thank you