Trust me vikpaw, we've tried every known solution to mankind (womankind too) to no avail. Simsperm didn't help, but thanks anyway. We can avoid it if a Local Admin logs in to sims on the exams PCs before a user, but that's a pain and not always possible.
We're moving sims onto a different network over the next year or two, so hopefully the problem will go away, but I'll be watching this thread closely.
Incidentally, can I private message you via this website? Your location is of interest to me and I can't use msn or skype.