system
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Oops! I should’ve told you to download the avast! uninstall tool and run it. :-[ My fellow avast! Evangelists should’ve reminded me.
http://www.avast.com/uninstall-utility
ZA has a built-in uninstall tool that runs automatically whenever ZA is uninstalled. 
Sometimes software becomes corrupt, it can happen to any software.
It’s good to run a software’s uninstall tool (if there is one) whenever you uninstall or re-install software.
Doing so can reduce problems.
I think it would be a good idea if avast! would follow ZA’s lead in including a built-in uninstaller that runs automatically on uninstall. 