Hmm... I do not know if the lack of Script Shield has anything to do with it though.
Repair Avast!
With XP
Start > Control panel > Add & Remove programs > select Avast! and click " Change/Remove ". Look for " Repair " and click it.
With Vista, win7, and W8 ?
Start > Control Panel > Programs > Programs & Features > uninstall a program > select Avast! and click " Uninstall/Change ". Look for " Repair "
Reboot when finished.