Assume it's Win 7 SP1? Difficult to say really, could be overheating, maybe low memory? Try running MVT: http://mvt.mcafee.com/ I assume it will run on a MAC to see if it will fix anything. Failing that you could try uninstalling in the normal way, running MCPR cleanup (link under Useful Links at top of page), rebooting and reinstalling as there was a problem DAT update over the weekend that caused all kinds of issues. If that doesn't help I would open a case with Technical Support, it's free by phone or online chat and available also through Useful Links above.