I had this very same problem. Found this on Technet forums:
http://social.technet.microsoft.com/Forums/en-US/configmanagerosd/thread/949574ac-c947-4ff4-a817-263014246ee2
More specifically, I hadn't added a boundary group to the distribution point. After that it worked fine.
Still trying to understand all the relationships of some of the new features of SCCM 2012 but it's been a good learning experience.