Unable to modify OfferAnswerNegotiation of session UCMA 4

Hi,

I am writing a UCMA 4 app.

In the app i am modifying the applicationendpoint.InnerEndpoint.SessionRecieved and adding a event handler.

in the handler i am modifying the OfferAnswerNegotiation of the session to a custom class created out of IofferAnswer. the moment i change the property i get hit with this exception. Unhandled Exception: System.InvalidOperationException: Must use IOfferAnswer interface or OfferAnswerNegotiator but not both.

please help.

Regards

Ankur