What phone? Android or iOS? Are you sure you are logging in properly? Make sure you are not clicking on the Register button underneath the user/password section, but click on the login button once the keyboard if hidden.
Can't log in using IOS ....getting an Error message saying I can not establish communication with the server. I'm currently using IOS 7.1.2. and my software says its up to date, but I know there are newer versions.