a61, if you messed up anything in the beta version, try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).
Actual version is 4.5.497 
Instructions to update here: http://forum.avast.com/index.php?board=11;action=display;threadid=8044;start=0
The email checking of avast changed completely from version 4.1 to 4.5.
Now it uses a new mail detection that will work automatically. Please, set up your email account just as avast does not exists. It will detect the pop3/smpt/imap ports and scan your messages.