I just managed to post without a problem?! Try forcing a refresh of the page and if that does not work, clear your Internet temp files from the Tools->Internet Options menu in IE.
I'm moving this to the Help: Mod Implementation forum, since this is a modded forum. I posted again and I do not see any problems with the basic functionality of post.asp to post messages. Maybe there are others, but as far as I could test it, there no problems posting messages.