The CPL_STOP message is sent once for each application when Control Panel ends.
lParam1
Specifies the application number. This number must be in the range zero through one less than the value returned in response to the CPL_GETCOUNT message (CPL_GETCOUNT – 1).
lParam2
Specifies the application-defined value loaded in the lData member for the application.
The Control Panel DLL returns zero if it processes this message successfully.
In response to this message, a Control Panel DLL should perform application-specific cleanup.