title: Ajax xMlHttpRequest.responseText not display what I set (very strange!)
body: <p>I have a standard Ajax call with "Success" and "error". The error part is as straightforward as:</p>
  
  <pre><code>error: function (xMlHttpRequest, textStatus, errorThrown) {
                   errorLabel.text("ERROR:  " + xMlHttpRequest.responseText); },
  </code></pre>
  
  <p>And in my C# backend, I saw someone recommend to use these code:</p>
  
  <pre><code>Response.StatusCode = 409; //as long as not 200
  Response.Clear();
  Response.Write(msg);
  Response.End();
  </code></pre>
  
  <p>My errorLabel successfully display xMlHttpRequest.responseText after validation ON MY LOCAL DEV MACHINE.</p>
  
  <p>However when I publish everything to a WINDOWS 2012 SERVER, there is no customized 'msg' in xMlHttpRequest.responseText anymore. Instead I got "<strong>The page was not displayed because there was a conflict</strong>" in responseText. (I could understand that status code 409 means there is a conflict.)</p>
  
  <p>So how come it will perform like that when on a server ?? My own error message seems to have been replaced!</p>
  
  <p>Thanks a lot!</p>
  
  <p>***********************  C# Code ******************</p>
  
  <pre><code>[HttpPost]
  public ActionResult DoSomething()
  {
      if (someconditiontrue)
      {
         return Json(new {value1=xxxx, value2=yyy})
      }
      else
      {
         Response.StatusCode = 409; //as long as not 200
         Response.Clear();
         Response.Write("my customized error message");
         Response.End();
      }
  
      return Content(string.Empty);
  }
  </code></pre>