CraigB
9
Very strange! is there any other security software installed? if there is no other security that might conflict then I would suggest doing a clean install by uninstalling your current version then reboot and run the avastclear tool http://files.avast.com/iavs9x/avastclear.exe which will automatically reboot the system to safe mode when run, make sure to run the tool for all versions of avast ever installed.
Once that is completed and rebooted back to normal mode then go forward with doing a custom install of the latest version.