Thanks, that worked.
It would be really nice to have a more meaningful error message. (otherwise my gut response is "No, you stupid bastard server, I don’t care, this is what I wanted to post! So #@$@#% off!)
It would also be nice to be able to configure it so that it was just a warning that appeared once, and if you really wanted to post, then you could click “No, I really mean it!” and post your content anyway.