got same error on win xp… so far here’s how i solved it.

  1. I downloaded the avast uninstall utility, run it under safe mode.
  2. once avast is uninstalled, i download a full avast 9 installer via oldapps.com http://www.oldapps.com/avast_antivirus.php (this is a safe site - i’ve been using this site to download old and latest full version of apps)
  3. install the latest full version, and register it with an email address.
  4. thats it! no more errors now.

I believe the error happens when update it via your old avast or those quick online setups. You definitely need to download the full installer to avoid errors.

hope this helps.