If you receive this message when you attempt to log in do the following.
Delete all old cookies from ar15.com.
Type in your e-mail address and password. Do not copy paste them as this doesn't always work.

Mobile devices.
Empty the cache on your phone and type in your log in information.

If you recently changed the e-mail address in your account you will be logged out and a server generated e-mail will be sent to your new address with a temp password.
Check your spam folder for it.