Thanks for the tip Edward, but the error persists.
DCOM, reported as a cause of C0000005 errors is installed because I've checked my W95 registry, as Ed Rauh advised.
Specifically, when CLEAR ALL is executed, it activates my Mainmenu.Unload event which does 'RELEASE WINDOW mainmenu', then executes the remaining commands in shut_dwn.prg. But when it hits QUIT, I get the C0000005 error which says the error was 'Called from - ' line 6 in Mainmenu.spr (DO FORM "mainmenu.scx" NAME _S3F0YPVGF LINKED TO m._rval) and from line 187 from my 'set main' main.prg (DO mainmenu.spr).
Franz, do you mean SP3 for VisualFoxPro6 or SP3 for NT?