I had a failed update some time ago. I decided to uninstall and just install the latest version. The uninstall could not complete. I was having trouble with some other things affecting reboots, and using system restore a lot to restore the configurations the way I wanted. Now, after using CC Cleaner and Windows One Care
http://onecare.live.com/site/en-us/default.htm several times, my restart works normally. Haven't turned my attention to see what is currently the status of AVG. Before, if I tried to install it or any other anti-virus, the error message indicated there was a file waiting for deletion upon restart.
Here's one solution. I haven't tried it, but renaming the problem file makes sense:
http://www.winhelponline.com/blog/error-invalid-update-control-ctf-file-when-updating-avg-anti-virus-80/