I have the simmilar problem (I get the error BAD REQUEST (INVALID VERB) and I don't know if this has something to do with the script, when you are posting postst, containing URL's (links). Is it possible, that URL is making this error.
Is there some problem with server IIS (I read something about that, but I am not very familiar with that issue, so I am just guessing.
I wan't to add that this error is not happening only when you create new message, but also when you reply to post, especially (or exclusively) when you post message with links.
It is strange, that when you post new post or reply and get this message Bad Request (Invalid verb), you can post it again, and then everything is fine. I really don't know, what is causing that problem.