system
8
I have a similar problem - tried the solutions mentioned above more than once.
Also tried this suggestion:
Try a clean install.
Download and save http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe
http://files.avast.com/iavs5x/avast_pro_antivirus_setup.exe
http://files.avast.com/iavs5x/avast_internet_security_setup.exe
http://files.avast.com/iavs5x/avast_premier_antivirus_setup.exe
Download and save http://www.avast.com/uninstall-utility
Reboot into safe mode>Run uninstaller for each version of avast you have>reboot into normal mode>install the version of avast you selected
above>register(Free)/insert license (Pro, AIS or Premier)>reboot 
So far I have spent the better part of a day trying to find & fix this problem with no forward progress to show.
Thanks for any help to get traction.