I've wrestled with FCFW for a year now and it's been disappointing that the author is AWOL. It was mostly working but with lots of errors being thrown up.
I finally decided to give up on it, and followed the instructions here to replace it:
This works perfectly, with no errors, however, the downside is that I lost all my FB comments from the past year. Big bummer, but nothing I can do. The FCFW plug-in did not give me any clear way to retrieve my XID, which presumably is the missing piece of the puzzle that would allow me to get all the old comments back.
Anyway, I thought I would post the TutsPlus link so that others can finally get on solid ground with FB comments in WordPress.