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:
Not Acceptable
An appropriate representation of the requested resource /forums/posting.php could not be found on this server.
Re: Problem replying to a specific post
Re: Problem replying to a specific post
Now, that was my first thought - but there really isn't anything in the post that could remotely be considered insecure.

I just attempted to include the original post here, and it failed with the same error.
So,
- if it's a security filter then it should at least state so and preferably indicate which part of the text was offending
- this post really shouldn't have triggered anything security-wise - i can email you the text if you're interested - so who knows what other perfectly innocent post could be getting rejected?