远程服务器返回错误401未授权的Webexception（POST）

Question

我正在尝试解决一个我最常见的问题（70％）（30％是成功的）。

我尝试使用以下代码执行webrequest（POST）：

private string HttpWebRequest(string busStopCode)
    {
        //XML input
        string xml = "<?xml version='1.0' encoding='UTF-8' standalone='yes'?><Siri version='1.0' xmlns='http://www.siri.org.uk/'><ServiceRequest>                              <RequestTimestamp>2011-10-24T15:09:12Z</RequestTimestamp><RequestorRef><username></RequestorRef><StopMonitoringRequest version='1.0'>                                 <RequestTimestamp>2011-10-24T15:09:12Z</RequestTimestamp><MessageIdentifier>12345</MessageIdentifier><MonitoringRef>"+busStopCode+"</MonitoringRef></StopMonitoringRequest></ServiceRequest></Siri>";
        string responseFromServer = null;

        // Create a request using a URL that can receive a post. 
        WebRequest request = WebRequest.Create("http://<username>:<username>@nextbus.mxdata.co.uk/nextbuses/1.0/1");
        // Set the Method property of the request to POST.
        request.Method = "POST";

        request.Credentials = CredentialCache.DefaultNetworkCredentials;
        // Create POST data and convert it to a byte array.
        string postData = xml;

        byte[] byteArray = Encoding.UTF8.GetBytes(postData);

        // Set the ContentType property of the WebRequest.
        request.ContentType = "application/x-www-form-urlencoded";

        // Set the ContentLength property of the WebRequest.
        request.ContentLength = byteArray.Length;

        // Get the request stream.
        Stream dataStream = request.GetRequestStream();

        // Write the data to the request stream.
        dataStream.Write(byteArray, 0, byteArray.Length);

        // Close the Stream object.
        dataStream.Close();



        // Get the response.

        WebResponse response = null;

        while (response == null)
        {
            try
            {
                response = request.GetResponse();
            }
            catch (Exception e) 
            {
                MessageBox.Show(e.ToString());
            }
        }


        // Display the status.
        MessageBox.Show(((HttpWebResponse)response).StatusDescription + " Completed");

        // Get the stream containing content returned by the server.
        dataStream = response.GetResponseStream();

        // Open the stream using a StreamReader for easy access.
        StreamReader reader = new StreamReader(dataStream);

        // Read the content.
        responseFromServer = reader.ReadToEnd();

        // Clean up the streams.
        reader.Close();
        dataStream.Close();
        response.Close();

        return responseFromServer;

    }

当我调用此函数时，我主要得到一个异常的消息框：

"System.Net.WebException: The remote Server returned an error(401) not authorized with System.Net.Http.Webrequest.GetResponse() with WindowsFormApplication1.Form1.HttpWebRequest(string BusstopCode) in <my pathfile>...."

我做错了什么？

我已经尝试过以前线程的几个解决方案，但没有成功......

谢谢！