I have the EXACT same problem. Since my subscription to avast! Internet Security was about to expire in 7 days, I decided to uninstall it and install the free version instead. I un-installed avast! IS via the Windows Control Panel, then ran the avastclear.exe program in safe mode, then ran avast Clean Up tool 1.3 (by Razor) also in safe mode, rebooting after each program.
I then installed the latest version of avast! Free and rebooted. Everything appears to be working fine, BUT for this problem.
Sorry I couldn't offer you any help. Let us know if a repair resolves your problem . . . .