Why am I getting this message: “Need to login from a specific client”

This occurs when you have an Android-only membership and try to log into it with a different username. Your membership plan allows you to log in with your mobile device, with the username you created when signing up. You have the option to upgrade to a full membership, unlocking your account so that you can log in from your desktop, notebook, mobile device, and from different usernames. Upgrading has other membership benefits, which can be found here.