HTTPWEBREQUEST 操作超时很费解

 我在模拟请求[POST]一个网站的时候，一直连接不上去，总是提示我”操作超时“
  HttpWebRequest httpWebRequest = null;
            HttpWebResponse httpWebResponse = null;
            try
            {
                byte[] byteRequest = Encoding.Default.GetBytes(postData);//格式化POST数据

                httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);//发送请求
               // httpWebRequest.CookieContainer = cookieContainer;//填充COOKIE
                //httpWebRequest.ContentType = "application/x-www-form-urlencoded";
                //httpWebRequest.ServicePoint.ConnectionLimit = maxTry;
               ;
                //httpWebRequest.Headers.Add("Accept-Language", "ko,zh-cn;q=0.5");
                //httpWebRequest.Headers.Add("Accept-Encoding", "gzip, deflate");

               // httpWebRequest.Referer = "";

                //httpWebRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
                //httpWebRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1; rv:20.0) Gecko/20100101 Firefox/20.0";
                httpWebRequest.Method = isPost ? "POST" : "GET";//那种请求？
                httpWebRequest.ContentLength = byteRequest.Length;//获取数据包大小

                Stream stream = httpWebRequest.GetRequestStream();//获取流对象
                stream.Write(byteRequest, 0, byteRequest.Length);
                stream.Close();

                httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                //定义数据响应信息
                Stream responseStream = httpWebResponse.GetResponseStream();//获取服务端回发达留信息

                StreamReader streamReader = new StreamReader(responseStream, encoding);

                string html = streamReader.ReadToEnd();
                streamReader.Close(); 
 
                responseStream.Close();
                currentTry = 0;

                httpWebRequest.Abort();
                httpWebResponse.Close();

                return html;//获取 
            }
            catch (System.Net.WebException e)
            {

Stream stream = httpWebRequest.GetRequestStream();/这句就出问题了
代码片段。HEAD头没问题，我用第三方 POSET模拟软件（HTTPAnalyzerFullV自带）提交的时候HEDA头什么也不设置值提交返回正常（也就是说提交的时候只有一个POST地址。和一个HOST主机属性，）而我用HTTPWEBREQUEST却怎么也访问不了
我抓POST模拟器（HTTPAnalyzerFullV自带）返回的包的时候发现返回头信息有

Expires-1 这个标识 难道跟这个有关系？如果有关系HTTPWEQUEREST 应该怎么设置。呢

[解决办法]
“抓包”时到底看到返回了什么呢？