It was there, then went away?  Or maybe never showed up?

Have you checked the "View My Posts?" queue?  There is a button on the top right of the message boards, and it will list all of your posts and their status.  "Not Allowed" means it was either never posted, or pulled after posting.

"Not Allowed" posts will also have a reason attached to them.  Check it out, and if the reason is unclear, please feel free to contact me.