高手帮忙看看模拟发布的问题

可以通过登录验证，也可以获取到需要登录的页面内容，但发布不成功，返回的和直接访问页面的一样，请帮我看看哪里出了问题。string url = "http://t.sina.com.cn/mblog/publish.php";
            HttpWebRequest requestScore = (HttpWebRequest)WebRequest.Create(url);
            string postData = "content=" + content + "&pic=&styleid=1&retcode=";
            //ASCIIEncoding encoding = new ASCIIEncoding();
            byte[] data = Encoding.ASCII.GetBytes(postData);            requestScore.Method = "Post";
            requestScore.ContentType = "application/x-www-form-urlencoded";
            requestScore.ContentLength = data.Length;
            //requestScore.KeepAlive = true;            //使用登陆的cookies通过接下来的验证
            requestScore.CookieContainer = container;
            Stream stream = requestScore.GetRequestStream();
            stream.Write(data, 0, data.Length);
            stream.Close();
            HttpWebResponse responseSorce = (HttpWebResponse)requestScore.GetResponse();
            StreamReader reader = new StreamReader(responseSorce.GetResponseStream(), Encoding.UTF8);
            try
            {
                return reader.ReadToEnd();
            }
            catch { return "\r\n"; }