I stopped as soon as I saw Norton. Uninstall it, run SymNRT, and install a real antivirus like Microsoft Security Essentials. Also, did you try VirusTotal and see what it had to say?
I tried this on the official IPS forums (the people who make this board) and my own forums as well. When I searched for just javascript the same error was returned. It's most likely a type of exploit protection built in.
That's because we went from 3.0 to 3.1 and the way SEO/SEF urls are have changed some, which is causing more bot/spider activity on the forums which makes them feel slower for now. It will pass in time, as 3.1 performs better than 3.0.
I don't care for, nor touch or really recommend their products after all the shady things they've done, especially issuing security/SSL certificates to websites with well known malware.
Downgrading from 7 means you'll be even more insecure. Also, Combofix is very dangerous to use. Perhaps you should follow the directions in the pinned thread.