jqXHR - http-status-code-403 (but the statuscode is 0)

i get the statuscode 0 ... but it is the code 403. Can someone tell me what the problem is?

JQUERY

  var jqxhr = $.ajax({
        url: 'http://gdata.youtube.com/feeds/api/users/bernd/favorites?alt=json',
        dataType: 'json'
    }).success(function(xhr) {
        alert(xhr.status);
    }).error(function(xhr) {
        alert(xhr.status);
        return false;
    })

DEMO -> http://jsfiddle.net/QFuBr/

Thanks in advance!
Peter