Well that's funny, since when do mail clients use the ports 6881, 6882, 6883 and 6884? The fix has worked, and I've got all my P2P clients using the above ports only. There seems to be a bug in the latest avast! that doesn't like P2P clients.
EDIT: There is also the fact that avast totally ignores what you do with the error box. if you don't answer it, another one will pop up X minutes later, if you click yes, another one will pop up X minutes later, if you click no, guess what? another one will pop up.