Hi,
I got the same problem on several computers ghosted, the installation floder was the standard one.
At: C:\Program Files\Alwil Software
The security tab grants full access at everyone.
At: C:\Program Files\Alwil Software\Avast4
Only the SYSTEM local accunt has access.
I tried to check the box: reset right on all child at the C:\Program Files\Alwil Software folder then it worked again. But the right were erased again by launching and update.
I am tring to find a workaround: I gave the READ right to the local and network user, i will see if next update the right have gone to SYSTEM or kept.
BTW: The machine are full NTFS and in a domain.
Hope it will be fixed soon.
