When you get this error, check these two things.
1. You did not activate your Flight1 account by clicking the email activation link sent to you when you opened your account. If this happens, you can still login to your Flight1 account, even though it is disabled. There will be an option to resend your activation link. Make sure you check any spam protection folders in case the mail gets intercepted.
2. Make sure you have the correct password. Go to the Flight1 account page at http://www.flight1.com/login.asp. There is an option there to help you if you forgot your password.