I have Xp and got this on an old computer, a restart usually cleared the problem, but the next time I started the computer would sometimes appear again, it is not always a problem, however, I uninstalled Avast, removing all traces using Revo and re-installed it. So far I have had no problems. The old computer does have it does have Sp3 on it, so try a clean Install.
I also got it once with Windows 8.1 but a restart solved it and I have had no more problems.
I am fully up to date with Avast and MS updates, though I see some waiting for 8.1 today
Away to get them into that computer now.