I have never seen any other report on the forum of rapport stopping avast updating.
avast does alert to each new version of rapport cerberus on my xp machine (not on w7 64 bit). I believe this is the rootkit scan. The filepath looks fine though, and a right click scan says clean, so I choose ignore. VT says the file is clean too.
rapport also blocks the avast behaviour shield injection of dll’s into browsers to monitor them. If you report it to trusteer they will whitelist avast, but the next program update re-introduces the problem, so I’ve stopped bothering to report it.