OS = Operating System and as you now said it's ME, which we now know can't be set to perform a boot time scan by avast. This is why the the option is grayed out.
I couldn't find RajZor external control menu.
You need to download the program using the link in RajZors signature (bottom of each of his posts).
lack of answers basically has come from me not really knowing what I'm talking about.
Which is why I gave you the link to the User's FAQ in my first post, if you didn't find it check for the link again (click the text User's FAQ in the post). There is a lot of information that will be useful for you in the future.
Now you know a little more should this happen again.
I wouldn't recommend not having System Restore always disabled. I don't use mine as I use a program that takes an image of my drive and if I have a problem I re-install the previous image, but I still have it enabled on my system.