title: jQuery ajax error callback not firing
body: <p>I am requesting a URL with ajax that results in a HTTP header code 500. I would expect this to trigger the error function: </p>
  
  <pre><code>    $.ajax({
    url: "http://xxx",
    dataType: "jsonp",
    crossDomain: true,
    success: function( data ) {
          alert('success');
    },
    error: function () {
          alert('error');
    }
  });
  </code></pre>
  
  <p>This works in safari, but fails in chrome and firefox. </p>
  
  <p>What am I doing wrong? </p>
  
  <p>This is the latest jquery 1.4.X, for reasons I cannot upgrade to later versions..</p>
  
  <p>The response sends a HTTP code 500, content type application/json and contents: </p>
  
  <p>jsonp1310063232212({"error":{"reason":"User not found"}})</p>