Star Wars: The Old Republic To Change Its User Login Credentials
Starting April 2, you won't be able to log into Star Wars: The Old Republic using your e-mail address. You'll have to use your display name. The change is being made in the interest of further protecting user information.
"This change increases the security of our game authentication system, which helps continue to keep the game protected from many security threats including account takeovers."
If you're not sure of your display name, you can head to StarWarsTheOldRepublic.com, log in as you normally would, and your display name should appear in the top right corner of the website homepage.