Norton tends to be a little thirsty on resources, so I would suspect that installing Norton as made a change to your previous configurations, hence microsoft wants to report a fault.
Do you have SP1 or SP2 installed, and what other security/protection are you running.
Norton have a very good knowledge base on their support website, with over 788 Microsoft FAQ's. Might be worth a look there.
Sorry that I cannot help further, but I usually ignore microsoft report notices.