I'm getting this same error. I've recently installed a fresh copy of Win 7 Ultimate x64 and have updated it and installed a few basic programs (EaseUS ToDo Backup, TeamViewer, Defraggler, Sandboxie, Comodo Firewall).
I can't see that Visual C++ is installed though. It seems strange that if this is required by Avast that it wouldn't notify the user or install it automatically but anyway, should I install 2008, 2010 or both?