Go to http://support.microsoft.com/kb/949377/ and use the Method 3 by downloading Subinacl.exe from Microsoft

IMPORTANT: Backup the registry before doing the above.
How to backup the registry: http://www.microsoft.com/downloads/details.aspx?FamilyID=e8ba3e56-d8fe-4a91-93cf-ed6985e3927b&displaylang=en
Or use Erunt to backup the registry: http://www.larshederer.homepage.t-online.de/erunt/

See also the existing discussion on similar issue at AVG Free forums:
http://freeforum.avg.com/read.php?13,138784,138784#msg-138784