Why does the site say my email is already registered?
If you are seeing a form like the one below, you may already be signed up:
This form is for signing up for a new account, so it is stopping you from creating an account with an email you have already used.
The best course is to login to the site instead. Either click "Sign In" at the top of the page, or use the "Already a member? Sign In Here" link. If you have not yet completed the payment portion of signing up, it will walk you through that step before taking you into the site itself.