Have a look on the Mac in the profiles, see if one of them is blocking it. I found with some things the profiles were blocking things even though you cant set them in there. The iSight camera is set using Restrictions, but the Security & Privacy will block it unless you have both in the configuration together. Maybe it is the same with FUS.
I just discovered that I am having this issue as well. I have FUS enabled on all of my profiles (because of the nature of the computers on our campus) and yet, I have a number of computers that I cannot get FUS to turn on. I am not seeing a profile that is disabling it... Any ideas where to look?