As of April 1, 2015, AOL Usernames can no longer be used to sign in to the iTunes Store. If you didn't manually convert your AOL Username before April 1, your Username has been automatically converted to an Apple ID.
Converted AOL Usernames will be your AOL Username plus an email address ending. For example, if your AOL Username was jappleseed, your new Apple ID will look like one of the options below:
If you didn't convert your AOL username before April 1st, the next time your try to sign in you'll be presented with your new Apple ID. You'll also be prompted to reset your password.
Take a look at the screenshot below for more details...