获取错误:远程服务器返回错误:(401)未经授权，同时在twitter上发布我的网站评论.使用C#

我试图在我的推特墙上发布我的网站评论，但我收到了一个错误

远程服务器返回错误：（401）未经授权的

我尝试过的代码是：-

using System;
using System.Web;
using System.Net;
using System.IO;
using System.Web.Script.Serialization;
using System.Text;
using System.Configuration;
namespace Dotned.UI.Framework
{
public class TwitterClient
{
    public string Username { get; set; }
    public string Password { get; set; }
    public Exception Error { get; set; }
    private string _twitterUpdateUrl = "http://twitter.com/statuses/update.json";
    public TwitterClient(string userName, string password)
    {
        this.Username = userName;
        this.Password = password;
    }
    public void SendMessage(string message)
    {
        try
        {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(_twitterUpdateUrl);
            request.Credentials = new NetworkCredential(this.Username, this.Password);
            SetRequestParams(request);
            string post = string.Format("status={0}", HttpUtility.UrlEncode(message));
            using (Stream requestStream = request.GetRequestStream())
            {
                using (StreamWriter writer = new StreamWriter(requestStream))
                {
                    writer.Write(post);
                }
            }
            WebResponse response = request.GetResponse();
            string content;
            using (Stream responseStream = response.GetResponseStream())
            {
                using (StreamReader reader = new StreamReader(responseStream))
                {
                    content = reader.ReadToEnd();
                }
            }
        }
        catch (Exception ex)
        {
            Error = ex;
        }
    }
    private static void SetRequestParams(HttpWebRequest request)
    {
        System.Net.ServicePointManager.Expect100Continue = false;
        request.Timeout = 50000;
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
    }
}
}

进程在WebResponse response = request.GetResponse();处中断。

任何建议都是非常可观的。