Since I posted this question, this issue has resolved itself. There must have been a glitch on Facebook or my dev server. Anyway, thanks to those of you who tried to help.
I have a Facebook app that runs on two servers: a live server and a dev server.
I was making some changes on dev and testing them when FBJS failed with an error (undefined functions)
I continuously reverted my changes to the dev server but could not get it working. So I reverted to the same revision that works on my live server, but it still fails on the dev server.
The source of the error appears to be a single JS file. I have verified in every way possible that this is the exact same file I am using on the live server where it works, but it is failing on the dev server with "undefined functions".
I am at my wits end with trying to debug this. I could really use some helpful suggestions. Thanks in advance for any help you can offer.
If you're interested in reviewing the apps, you can find there here:
Live: http://apps.facebook.com/rails_across_europe
Dev: http://apps.facebook.com/rails_dev
Note that you must give the app permission to access your FB profile data.