Sign-up form for Pro Sites returns "page not available."

I am setting up a user's site in my pro sites install. I clicked a "Pro Only" link on a theme and was directed to a Sign Up page that doesn't work. The problem (as personal as it may seem) is I can't remember if it was a page I created or if it was an auto generated page. I trashed it yesterday because it was blank, but restored it when I saw the link to it.

What is supposed to happen when someone clicks to preview a theme or click the "level only" link?