jQuery is not defined
This is because the Google CDN Jquery is not in no-conflict mode. Use the following to make sure the included WordPress no-conflict jquery is used in admin.
if( !is_admin()){
wp_deregister_script('jquery');
wp_register_script('jquery', ("http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"), false, '1.4.2');
wp_enqueue_script('jquery');
}