The "Mobile Locked" error occurs in response to multiple failed sign in attempts being made with your Yahoo! ID from a mobile device.

To resolve the "Mobile Locked" error:

1. Using a desktop computer, navigate to the Yahoo! sign in page.
2. Enter your Yahoo! ID and password.
   Note: If you are already signed in, first click Sign in as a different user.
3. Click Sign In.
4. Attempt to sign in on your mobile device again.