I have 3.5 but can't select Meta Files.

I want to set up external source control for our project, and was delighted to see several posts saying that Unity 3.5 Free now allows meta files. But when I go to Edit > Project Settings > Editor > Version Control, Meta Files are grayed out. The only selectable option is “Disabled.” Are the meta files just being generated automatically? Or is there something else I need to do to get them to work?
(I checked for updates and it says I have the most current version: 3.5.0b6.)

Thanks.

So in case anyone views this question later, that was the answer:
Version 3.5.0b6 was not the most recent version. Having the most recent version of Unity fixes the problem.