If you haven't upgraded in a while, you might want to take a moment to verify that your default profile (again, the one with your user name) is running 1.6.4. Thankfully, the new launcher provides us with an easy method to selectively change versions on the fly or download older ones.
You needn't worry about this for at least another week or two, but I'm posting this so that those of you who have been playing on occasion might mentally file it away for future use. This is especially true if you attempt to connect to the server only to find that your client refuses.
