This is a strange problem that just started yesterday. If I have more than 1 dwg open, and I try to close one of them, I get a fatal error "Unhandled Access Violation Reading (hexadecimal babble)". As long as I have "Single Drawing Compatibility" checked in Options, there's no problem, though, so it seems to be related to multiple dwg windows. In fact, I can have multiple drawings ENABLED and, as long as I only keep only one window open (which of course defeats the purpose of having multiple windows enabled) there's no problem. Has anybody else had this problem? I'm suspecting the o.s. (Windows XP Pro) at this point -perhaps a flaky Explorer.exe, but it could be AutoCAD, although I've replaced my Acad.exe with a backed up one, and the problem persists.