1. Have you tried to delete the temporary Internet files? To do this go to Internet explorer >Tools > Internet options > Delete files > Click delete all offline content (just to be sure) > click ok. It might take some time to delete them.

  2. Disable (and enable it after) System Restore: Start > Control Panel > System > System restore > Disable > Click Apply > Enable it again > Click Ok

  3. Schedule a boot-time scanning again: Start avast! > Right click the skin > Schedule a boot-time scanning > Select for scanning archives > Boot

Hope this helps…