I had Norton (notice I used the word HAD?) and I constantly had exactly that same kind of problem with it (FOR YEARS!) .. I finally got tired of messing with it, trying to fix it and now have Avast and am problem free. No more hours wasted trying to fix what I figure is a built in flaw.

Avast is FREE! A deputy sherriff told me about it, he has used it problem free for ages.. http://avast.com/ The home version is free, they make their money selling it to professionals.