Crashing when i am trying to wfcWAssembly::cast(CurrentModel);

I am trying to get list of display component so i am using 

pfcSession_ptr session = conn->GetSession();

pfcModel_ptr CurrentModel= session->GetCurrentModel();

wfcWAssembly_ptr WAsm = wfcWAssembly::cast(CurrentModel); 

but its crashing in last line not able to debug have anyone idea about this i am using this in asynchronous mode