This error is caused by a corrupted vvfolder.idx file located in the AVG vault folder. If you're using Windows XP or below, go to My Computer > Tools > Folder Options and select Show hidden files and folders from the View tab. If your computer runs Windows Vista or above, go to Start, type Folder Options and open the utility. Select the View tab and check the Show hidden files, folders and drives option. Click Apply and then OK. Delete all X:\$AVG8.VAULT$ folders from your hard drives and restart the computer.