We are sorry to hear that you are having this issue. The only time that you would see a message that your email address is already in use is if you tried to sign up for a new account. Since you have already created an account with your email address the system will not allow you to create another one with the same address. Make sure that you are not using the sign-up form to try to login to your existing account.
Click on the Login button. You should be able to login by typing in your email address and password into the pop-up box that appears. If you are still unable to access your account using the login box, please let us know.