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.
Also worth reading so you don't misuse the Hosts file like some sites recommend: http://wiki.lunarsoft.net/wiki/Blocking_Malware_and_Advertisements_Safely