Servo, perhaps you've already tried that, too, but have you reinstalled your OS, installed Carrara on it's own, fresh formatted partition before you installed anything else?
It may be a lot of work, but I had exactly the same problem some years ago with Poser 6 and this solved my problem (yes, I know, Carrara isn't Poser, but it's just an idea).
Hope this issue is eventually solved for your.

~Sassy~