When I go on a Minecraft PE server, I cant log in. It says that I am registered and have to log in, but I have never been on that server before. And when I try to type in login and just a random password, they say its wrong password.
This means that someone else has already registered this username on that particular server. In order to register you must change your username, log onto the server, and type into chat /register <>.
P.S. "<>" is usually a password or sometimes an e-mail and a password.