Have you been able to log in before? Or, is this your first time?
If this is your first time, than you might have to make a new account if your passoword has special symbols, or is much too long. The 'too long thing' goes with usernames aswell.
When it comes to the other way around, I'm not exactly sure how to fix that. It may be the servers glitching abit, but, check and see if you've had num lock or caps lock on without noticing.