HttpWebRequest.GetResponse()

HttpWebRequest.GetResponse() 报404错误
Excetion 报ProtocolError
抓包里Referer也没错
post过去也没错，没有参数直接提交。
不知道什么原因报错
原来用的好好的，突然不行了，要设置些什么吗？ request1.Method = "POST";
                    request1.CookieContainer = 共享的Cookie;
                    request1.Accept = "application/json, text/javascript, */*; q=0.01";
                    request1.Referer = 
                    request1.Headers.Set("X-Requested-With", "XMLHttpRequest");
                    request1.Headers.Set("Set-Cookie", "perm=1; Domain=域名; Path=/");
                    request1.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1";
                    request1.Timeout = Timeout.Infinite;
                    request1.AllowAutoRedirect = true;
                    request1.KeepAlive = false;
                    request1.ContentLength = byteRequest.Length;
                    using (Stream stream = request1.GetRequestStream())
                    {
                        stream.Write(byteRequest, 0, byteRequest.Length);
                    }                    response1 = (HttpWebResponse)request1.GetResponse();
                    Stream stream2 = response1.GetResponseStream();
                    using (StreamReader sr = new StreamReader(stream2))
                    {
                        resp1 = sr.ReadToEnd();
                    }
                    response1.Close();