easy,
I am not aware of any "bug" that relates to your problem, although some users have had such trouble.
Repairs usually resulted in a clear install of Avast then.
However, if you use XP, you can do an Avast Repair which usually corrects and repairs any files that have gone astray.
If you go into the Control Panel, Add/Remove and highloight Avast, you should see the Repair option come up (if you have it......W9x and ME OS will only remove Avast.......Not sure about Win2000).
Let me know what happens.
Techie