The email you are using to set up the database is also the email associated with your MyAdmin account. If you use your MyAdmin email, you must use your MyAdmin password. This system was implemented recently, which may explain why you have not encountered this error message previously.
A reseller can log in to any of their customers' databases using their MyAdmin credentials. This eliminates the need for resellers to manually create an account on each database.
Let me know if you need further information or clarification.