Hmm... as far as I know macally does very proper developing, and I almost can't believe that they produce a bug like this (even if the mouse driver permanently accesses its own extension file, there would be no problem moving the file with the manager). It really sounds like something else running havoc on your system in the background. Can you boot without extensions (eg by holding down the shift key on startup)? You might have trouble running Lightwave etc (because they might depend on certain extra extensions), but you can then do the switch in extension manager. If it still crashes then, it's almost certainly system re-install time...