We've run into this situation multiple times now on two different PCs - once on the first PC, and 5 or 6 times on a second PC. Both are running fully patched versions of Windows XP Pro, with SP1.3 applied to MSCAD.
At any given time, MSCAD will start to ignore commands, whether typed or chosen from a menu or toolbar. If it's one that we've chosen from a menu or toolbar, we'll see the command listed in the command window, but there's no response from MSCAD - not even an error message; we just get returned to the ":" prompt. The only way to fix it is to use the Task Manager to kill MSCAD, and then restart. Since the QSAVE command is ignored along with everything else, we can't even save the drawing that we're working on, and so lose our work since the last autosave. I haven't seen any other window/dialog box appear, or haven't been able to find one in behind another window that may be somehow stealing the focus and causing this problem.
We cannot reproduce this problem to test it. Has anyone else seen this, and have a fix for it?
Thanks,
Chris