Steve,
Looks like Facebook rolled out a bug yesterday that was fixed pretty quickly. We never saw the issue, but your the 2nd user to report the exact same error message on a site that was previously working. The other user said it corrected itself as well.
Facebook is constantly updating their Javascript API which can introduce issues, although uncommon. It sounds like you just got bit, temporarily, this time.
Of course, if it comes back or you run into other problems, just let us know.
Thanks,
Alex