system
2
Hi,
what virus was this exactly ??
what Win do you use ? are all Winupdates applied ?
Seemingly, some malware changed the system settings for opening EXE-files (programs).
so even the avast CLEANER cannot be run normally, but when you rename it to .COM, .SCR or similar,
it should run, detect the system/registry changes and repair them (restore them to the default settings).
So just do it… 
After a reboot, everything SHOULD run smoothly again…
Afterwards, run a thorough scan with avast (archive scanning enabled), and clean/repair/move any infections, in case there should be left any…
(see “VirusRemoval” below in my sig, also on how to secure your system & browser better…)
