I'd guess that AVG "hijack's" mailwasher's attempt to connect to port 110 so that it can intercept and scan incomming mail, perhaps this slows things down too much for mailwasher.
I know mailwasher dies if I have too much stored mail on the server, not tried it with avg as I only use mailwasher at work - where it saves me from about 200 spams a day
Have you tired tinkering with timeout settings on Mailwasher?