This message indicates that the email address being used to set up the account exists somewhere else in our database. Either the user in question is already a user on your account or they have their own account set up under that email address. It is not possible to use the same email username across multiple accounts so the primary or secondary account will need to use an alternate email address. If the second account they have is no longer needed by them, they can also cancel that account to free up their email address for use on the new account.