An application may use SetSuspendState to transition the system from the working state to the standby (sleep), or optionally, hibernate (S4) state. BOOLEAN SetSuspendState( BOOL Hibernate, BOOL ForceCritical, BOOL DisableWakeEvent );

Problem solved - I had declared the callback functions to return bool (as 'required' by some other hardware drivers) - changing the return type to LRESULT fixed the problem. I wonder why this compiled ok (I just checked it, it does) before I added the second inheritance?? Thanks for your help. Will