Registration Link broken again....?

We had this problem before, and back then it was related to the new theme updates etc. Now I'm not sure what's caused it to happen again, but the problem is back, on, you can't register. I've checked the settings, they all say registrations allowed. There's no error, it just redirects to the main page again. Entering in the address bar /register = Entering redirects to ??? Help. plz.