Norton antivirus is great. Norton internet security is not. You should use a hardware firewall (like a good router) and norton antivirus only.

Anyways...that aside, there should be a place where you can edit all the firewall rules in Norton internet security. You can search for .exe files to allow and explicitly add bitcomet's .exe to the list.

And as an aside, I'm sure you heard this before, but bitcomet has had a pretty bad track record of not following good torrent standards. Azureus and μTorrent are better choices.