You’re running an old version. version 6 has been out for a while
May I suggest that you try the latest pre-release version recently made available.
It’s running without any problems on my system and has solved many incompatibility issues.
You can read about it and download the version you’re currently using (Free - Pro - Internet Suite)
from here:
http://forum.avast.com/index.php?topic=73110.msg608535#msg608535