Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endRequest);

function endRequest(sender, args)
{
    // Check to see if there's an error on this request.
    if (args.get_error() != undefined)
    {       
        var errorMessage = args.get_error().message;
        if (errorMessage.indexOf("The status code returned from the server was: 0") != -1)
        {   
            args.set_errorHandled(true); 
        }
   }
}