One more time, in order to use the message function.
1.Delete all the messages between the two of you
2. Go to the person's profile page.
3. click on the message function there.
4. Type your message and send.
So far this is the only work around that works. If you are going to continue to communicate I suggest you exchange emails, throw away emails, or phone numbers.
A shame that developer guy, when he was online here a week or so ago, didn't do anything with the messenger. Nothing too much glitchy with the posts, but the messenger is sure messed up.