Since this also came up on the fw1-gurus mailing list, and a suggestion there was that you try this :
Logging to Syslog? and you are aware of that thread, having posted on it, have you actually tried the suggestion?
There was a rather unhelpful post in that thread saying "I can't do it. Fix it for me. Wah wah.", that didn't even bother describing basics like what wasn't working. It doesn't mean that you won't be able to get it working though.