Important: Purchasing a subscription does not create an Ultimate Guitar login and password for you automatically. Your subscription is attached to your Apple ID account and we recommend you to create Ultimate Guitar account in the app (it's free). This way your subscription and favorites tabs will be safely attached to your UG account and you won't lose them.
If the system does not recognize your email address it can mean that:
You've used another email at registration
You haven't created an Ultimate Guitar account yet
In the first case, please try all your email addresses that could have been used to create an account.