I'm not sure about what exactly you'd have to do within Norton Internet Security to fix the problem, but my advice (and I'm sure a lot of other people on here would agree, given the comments made in a
recent thread on Norton) would be to get rid of Norton completely and replace it with something else. Norton Internet Security is a complete drain on your system - it hogs a lot of your memory and CPU and in that respect is totally inefficient compared to many other products you could have (many of which are free.) When I removed Norton, it felt like having a brand new system - it was so much faster.
If I were you, I'd get rid of Norton. Download ZoneAlarm for firewall protection (free, and works with the latest Firefox update). With regards to anti-virus protection, I use Symantec Anti-Virus Corporate (free from my University) but there are some decent free virus checkers available on the net which will do the same job as Norton but more efficiently. I've heard AVG mentioned, there is a free version available
here.