Are you using MFC and custom message handling (ON_MESSAGE, ON_REGISTERED_MESSAGE) at all? If so, check that your handler functions for those messages are declared afx_msg LRESULT funcname(WPARAM,LPARAM) and not anything else. This is a common cause of "works in debug, crashes in release". Alternatively, modify your link properties to generate debugging information, and run the release version under the debugger. You can do this without turning off optimisations. This might help you find the area that's at fault. Steve S Developer for hire