Sounds like a bug, really.

Please try the following patch:

  1. Stop the avast antivirus service (Control Panel → Administrative Tools → Services)
  2. Download the file http://www2.asw.cz/~vlk/ahresmai.zip and extract its contents to the avast directory (overwrite existing files)
  3. Restart the avast antivirus service

That should help. Please let me know if it does.

Thanks
Vlk