If you get the error message "A user with this email address already exists." when trying to join the community ... and maybe you weren't expecting to join the community since you were previously an active member, there are some steps you can do to get reconnected with your account.
First of all click the "Cancel" button for joining in.
Then, click "Sign In" near the top right, then click the "Help" link, and then click "I forgot my password".
Fill out your email and click on "Recover Password". You will receive an email shortly with information on how to get into your account. You can continue to get into your account using the way described in this email.
If you'd like to associate your new GCX account with your TntMPD account, click "Edit" near the top right to edit your profile. Then click "Sign-in Information". Then you can click on "Associate GCX ID" to reconnect your TntMPD account with your GCX account.