C#/Asp.net 如何用HttpWebRequest Post自动登录、填表提交？

CookieContainer RequestCookies = new CookieContainer();
    protected void Page_Load(object sender, EventArgs e)
    {
        string username = "zhanghao";
        string pwd = "mima";
        string posturl = "http://my.anjuke.com/v2/my/login";
        string postdata = "loginpost=1&formhash=&history=aHR0cDovL3NoYW5naGFpLmFuanVrZS5jb20vdjIv&systemtime=1297321220&loginName=" + username + "&loginPasswd=" + pwd + "&remember=1&submit=";
        getMcc(posturl, postdata);
        
        postdata = "txtCommunity=德安大厦&radUseType=5&txtProFloor=1&txtFloorNum=2&txtAreaNum=30&txtRoomNum=1&txtHallNum=0&txtToiletNum=0&txtProPrice=50&txtHouseAge=2000&radFitment=1&radHouseOri=0&radCurrentState=1&txtUserDefine=zheshibeizhu&txtProName=zheshibiaoti&areaTplId=&commTplId=&txtExplain=<p>zheshimiaoshu</p>&radSaleType=2&hidact=save&hidBrokerID=667389&hidCommunityID=3726";
        posturl = "http://my.anjuke.com/v2/user/broker/property/sale/step1";
        getMcc(posturl, postdata);
    }
public void getMcc(string PostUrl, string PostData)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(PostUrl);
        
        if (!string.IsNullOrEmpty(PostData))
        {
            request.CookieContainer = RequestCookies;
            request.AllowAutoRedirect = true;
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)";             Encoding encoding = System.Text.Encoding.GetEncoding("UTF-8");
            byte[] data = encoding.GetBytes(PostData);
            request.ContentLength = data.Length;            Stream newStream = request.GetRequestStream();
            newStream.Write(data, 0, data.Length);
            newStream.Close();
        }
        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        Stream stream = response.GetResponseStream();        using (StreamReader read = new StreamReader(stream, Encoding.UTF8))
        {
            string strcontent = read.ReadToEnd();
        }
    }
我的代码如上  但是登录完成后提交发布的时候不行  怎么回事啊？  求教各位大侠！~~~~~~~