From the AVG forum:
You need to rename/remove the CTF temp files in C:\Documents and Settings\All Users\Application Data\Avg8\update\download…. Dont delete all the .bin files in there unless you want to re-run all updates since your original installation (reinstallation seems to cause a problem in IEs Link Scanner which causes IE to Crash). Only rename/remove the avginfo files that end with .ctf.
In Windows Vista, you simply need to move the two ctf file to other location in your hard disk (for backup just in case anything goes wrong) and this will fix that problem. It seems that the two old ctf files are not compatible with the newer AVG Anti-Virus updates, therefore remove the two file will force AVG Anti-Virus to download the latest one.