title: ASP.NET MVC3 AJAX.BeginForm AjaxOptions OnSuccess OnFailure Problem
body: <p>My question is what is condition for the OnFailure callback to be called , how does the runtime know the ajax call is failed (the ajax helper use some http response status code to indicate that? what it would be then?). 
  And if the html of UpdateTargetId is updated no matter the ajax call is failed or success, then how should I handle the error properly then. Very confused...</p>