When an ajax call returns 0 this usually means that you do not have your actions set up correctly. You will want to make sure that you are hooking into wp_ajax as well as wp_ajax_nopriv
add_action( 'wp_ajax_ACTION', 'your-callback' );
add_action( 'wp_ajax_nopriv_ACTION', 'your-callback' );
I would guess that the problem is that you are only hooking into wp_ajax and are logged in on your dev installation and you are not logged in on the live install. Just guessing here. Would have to see all of the code to know for sure.