Seems to be a strange problem with the forum.
I can't reply to this post: http://www.fckeditor.net/forums/viewtopic.php?f=6&t=10384
I can click "Reply" but then every time I click "Preview" or "Submit" I just get an Apache error screen:
An appropriate representation of the requested resource /forums/posting.php could not be found on this server.
I can reply to other posts and (obviously) post new replies with no problem!