Unfortunately, that link doesn't work. The only way to send a note to a player is to have it linked to a quiz. Either you reply to a note they've sent you, or you find a quiz of theirs and click on "Send a Message to Editor."
It's tedious, especially since many players haven't created any quizzes, but it is the only thing you can do.
What is this quiz of yours about? I'd be interested in looking at it. I hope you're enjoying your time in Quizzyland!