The FMEVENT_UNLOAD message is sent to an extension DLL when File Manager is unloading the DLL.
FMEVENT_UNLOAD
This message has no parameters.
An extension DLL should return zero if it processes this message.
The hwnd and hMenu values passed with the FMEVENT_LOAD and FMEVENT_INITMENU messages may not be valid at the time this message is sent.