I found that when I was already logged into my account and I clicked the link it took me straight to my account page. I was able to resolve that, though:
Log out of your NCSoft account. Then, click the link above, which will take you to a beta registration page. Click the link on the right-hand side of the page to login to your existing account. It should let you register for the beta, then, if you're not already registered. If you follow those steps and it still takes you to your account summary then you're probably already registered.
It's the "old sign up" if you already signed up through NCSoft, I would assume. When I signed up this morning through the link above, it didn't say anything about me already being signed up. I still have the original email from Carbine when I signed up through their website over two years ago, though.
Probably contributes to me never having received a key if beta access was handed off between the studio and publisher ;-)