Exception at get Silverlight request

Tell me why does Exception work?

(SYstem.Net.WebException: The remote server returned an error: NotFound. at System.Net.Browser.BrowserHttpWebReqest.InternalEndGetResponse(IAsyncResult asyncResult) at System.Net.Browser.BrowserHttpWebRequest.<>c__DisplayClassa. <EndGetResponse>b_9(Object sendState) at System.Net.Browser.AsyncHelper.<>c__DisplayClass4.<BeginOnUI>b__0(Object sendState) 

  _urlRequest = "http://localhost:3019/func.cshtml"; HtmlPage.Document.SetProperty("title", "Silverlight запрос и получение xml данных "); private void Button_ClickGraphAvto(object sender, RoutedEventArgs e) { divider = 20; HttpWebRequest ht = (HttpWebRequest)HttpWebRequest.Create(_urlRequest + "?req=avto"); IAsyncResult result = ht.BeginGetResponse(new AsyncCallback(RespCallbackXml), ht); } private void RespCallbackXml(IAsyncResult asynchronousResult) { try { HttpWebRequest ht = (HttpWebRequest)asynchronousResult.AsyncState; HttpWebResponse response = (HttpWebResponse)ht.EndGetResponse(asynchronousResult); Stream responseStream = response.GetResponseStream(); responseStream.Position = 0; StreamReader sr = new StreamReader(responseStream); string strXml = sr.ReadToEnd(); ShowString(strXml); ShowGraph(responseStream); } catch(Exception e) { ShowString(e.InnerException.ToString()); } }