I can't give you even a clue with Windows7 and IE8, although it will especially help the devs if you confirm as to whether it was the Temp Files clean or the registry "Issues" clean which you believe caused the problem.
it's the temp files (immediately after cleaning the temps, and not the registry, i checked) and i have yet to test which temp files are the issue for uninstalling/reinstalling certain progs 4 times to narrow it down aggravated me. so, i had to just put it down and walk away.
what other info is needed to narrow my issue down, if any? i'm no0b and don't have 2 separate setups to test my pc's simultaneously. so, i'll work on my "broke" pc after i get more knowledge in my predicament. or if AVG's temp files are the issue i'll just have to not clean it and wait for some sort of "fix."
If any more info is needed I'm sure they'll ask for it.
We have members on here who run Windows7 and IE8, but it isn't easy pinpointing what could be an issue between 3 applications.
You could just untick the items in CCleaner and then re select them one by one, but the result of the issue, ie having to reinstall, probably isn't something you want to repeat.
Hope that helps for now, unless someone else has experienced a similar problem, and may contribute.