I'm on a cable service, so I don't use the Norton firewall portion of their software - because I don't have to - and my ISP recommended that I don't because it conflicts with theirs. That might be something else you could check.
My auto updates run perfectly - and I have it set for a weekly scan automatically. I've never had any problems.
MacAfee is not that good - so I agree with RedWing9 regarding that software. And .. my son is a computer professional - he hates MacAfee.
my norton was running perfectly also, then it hiccups and i no longer have the auto run.