Crash trying to trigger an event in a PBNI object

I'm trying to create a visual PBNI object that will ultimately, I hope, allow me to subclass a window. Everything seems ok on the surface until I try to trigger a custom event on the object.

Then the application crashes.

The code fragment that defines the call (returned by PBX_GetDescription) is:

 _T("class u_x_subclasser from userobject\n") \   _T("   subroutine uf_start(unsignedlong wndhandle, unsignedlong msgid)\n") \   _T("   subroutine uf_end()\n") \   _T("   event long windowprocmessage(unsignedlong hwnd, unsignedlong msg, unsignedlong wparam, unsignedlong lparam, ref boolean callbase)\n") \   _T("end class\n") \

Note I'm defining an event called called windowprocmessage. If I leave out the part that tries to fire this event and import into Powerbuilder then I see the object with the defined methods and the event and it all looks ok and I can call the methods with no problem.

But as soon as I introduce the following code then I get the crash:

  pbclass thisClass = m_pSession->GetClass(m_pbobject);  pbmethodID mid = m_pSession->GetMethodID(thisClass, _T("windowprocmessage"), PBRT_EVENT, _T("LUUUURB"));  if (mid != kUndefinedMethodID)  {  try  {  PBCallInfo ci;  m_pSession->InitCallInfo(thisClass, mid, &ci);  ci.pArgs->GetAt(0)->SetLong((pblong)hwnd);  ci.pArgs->GetAt(1)->SetUlong(uMsg);  ci.pArgs->GetAt(2)->SetUlong(wParam);  ci.pArgs->GetAt(3)->SetUlong(lParam);  ci.pArgs->GetAt(4)->SetBool(*callbase);
//**** THIS NEXT LINE CRASHES!   PBXRESULT pbx_res = m_pSession->TriggerEvent(m_pbobject, mid, &ci);  // Was PB exception thrown?  if (m_pSession->HasExceptionThrown())  {  // Handle PB exception  m_pSession->ClearException();  }  *callbase = ci.pArgs->GetAt(4)->GetBool()? true:false; // Strange syntax but avoids pbboolean to bool conversion warning  returnVal = ci.returnValue->GetLong();  m_pSession->FreeCallInfo(&ci);  }  }

Any ideas?