system
3
EdB,
I had the same problem. Avast 2.5.x would pop up an alert and then freeze! 
I tried āRepairā from the installer script, but it didnāt help. I finally uninstalled Avast, rebooted, ran my favorite registry cleaner (JV16Powertools), rebooted, downloaded and installed the latest version of Avast and the problem was solved. ;D
Sometimes itās easier to just start over.