I don't really know what else to suggest as the suggestions have usually been enough to resolve the problem in the past.
You aren't using any VM software as I think there might have been something about updated issues with VM software ?
I take it you have an admin privilege and UAC doesn't get in the way ?
Other than that all I can suggest is try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow.
If that doesn't work try, uninstall, reboot, install, reboot. Because you are using the beta version you will probably need to run the uninstall utility to ensure nothing remains in the registry.
Download the latest regular release version of avast 4.7.1074,
http://www.avast.com/eng/download-avast-home.html and save it to your HDD, somewhere you can find it again. Use that when you reinstall. If you wish to continue with the beta trial you would also have to run the aswbeta.exe installation file again.
Download the avast! Uninstall Utility,
find it here and save it to your HDD.
Now uninstall, reboot, run the uninstall utility, reboot install the latest version, reboot.