The problem was with McAfee, not Norton. It was big news a couple of days ago:
http://news.cnet.com/8301-1009_3-20003074-83.html
Are you running McAfee anti-virus?
Try this if so (note I haven't tried it myself, I don't use McAfee):
http://brianseekford.com/index.php/2...nition-update/