Can't setup scanning during boot...

…because the option is just inactive. I use avast! 4.8 Home Edition on Windows Vista x64 Premium and I used to take advantage of this feature in the past. I would be grateful for any ideas how to enable that thing [the problem doesn’t disappear even after turning the UAC off].

Hi catviz,

Welcome to the forum.
Short answer: boot-time scan is not supported with either XP or Vista 64-bit OS

It will be supported only on avast 5 version, next July.