c# – Http post error：远程主机强行关闭现有连接

Unable to read data from the transport connection: An existing
connection was forcibly closed by the remote host.

下面是我目前使用的代码,但我已经尝试了几乎所有我能想到的不同方法,它们都返回相同的错误：

string result = "";

        string xml = "<TNSAuthRequest><CardNumber>0123456789</CardNumber><ExpiryDate>1801</ExpiryDate><PurchaseAmt>750</PurchaseAmt><CurrencyCode>826</CurrencyCode><CurrencyExponent>2</CurrencyExponent><CountryCode>826</CountryCode><MerchantName>Mayflower</MerchantName><MerchantId>0123456789</MerchantId><MerchantData>abcdefghijklmnopqrstuvwxyz0123456789</MerchantData><MerchantUrl>example.com</MerchantUrl><NotificationURL>example.com/basket</NotificationURL></TNSAuthRequest>";

        var url = "https://mpi.securecxl.com";
        byte[] bytes = System.Text.Encoding.ASCII.GetBytes("xmldata=" + xml.ToString());

        ServicePointManager.ServerCertificateValidationCallback += new System.Net.Security.RemoteCertificateValidationCallback(ValidateRemoteCertificate);

        var req = (HttpWebRequest)WebRequest.Create(url);
        req.AllowWriteStreamBuffering = true;
        req.ContentType = "text/xml";
        req.Method = "POST";
        //req.ContentLength = bytes.Length;
        req.KeepAlive = false;
        req.ProtocolVersion = HttpVersion.Version10;
        req.ServicePoint.ConnectionLimit = 1;
        //req.Timeout = -1;

        try
        {
            using (var writer = new StreamWriter(req.GetRequestStream(),Encoding.ASCII))
            {
                writer.WriteLine(bytes);
            }
            using (WebResponse resp = req.GetResponse())
            {
                using (StreamReader sr = new StreamReader(resp.GetResponseStream()))
                {
                    result = sr.ReadToEnd().Trim();
                }
            }
        }
        catch (Exception ex)
        {
            result = ex.Message + "<br />" + ex.InnerException.Message + "<br /><br />" + xml.Replace("<","&lt;");
        }

        ViewBag.result = result;

如果任何人都可以看到可能导致此错误的代码可能出错的任何内容,或者如果它最有可能在他们的结尾出现问题,我基本上会徘徊吗？尝试在我的localhost,我们的实时服务器和我自己的私有服务器(具有完全不同的IP)上运行,并且仍然得到相同的结果.

有任何想法吗？