Did you register using Google Sign Up and now your Google email address have changed?
As long as you still can receive emails on the original email address there is a solution.
1. Generate a password to your old email address by clicking the "Forgot Password" button on the Login page.
2. When the new password is set and you are logged in. Go to the User Settings (click your name / email address on the top right) and request to change email to your new Google email address.
After the email is updated you can login using Google login and your new email address.