Posting feeds from my website to twitter is not working

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net;
using System.IO;
using System.Xml;

private static void PostTweet(string username, string password, string tweet)
    {
        try
        {
            // encode the username/password
            string user = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(username + ":" + password));
            // determine what we want to upload as a status
            byte[] bytes = System.Text.Encoding.ASCII.GetBytes("status=" + tweet);

            // connect with the update page
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://twitter.com/statuses/update.xml");
            // set the method to POST
            request.Method = "POST";
            request.ServicePoint.Expect100Continue = false; // thanks to argodev for this recent change!
            // set the authorisation levels
            request.Headers.Add("Authorization", "Basic " + user);
            request.ContentType = "application/x-www-form-urlencoded";
            // set the length of the content
            request.ContentLength = bytes.Length;

            // set up the stream
            Stream reqStream = request.GetRequestStream();
            // write to the stream
            reqStream.Write(bytes, 0, bytes.Length);
            // close the stream
            reqStream.Close();
        }
        catch (Exception ex) {/* DO NOTHING */}
    }