贝宝集成时出错

我试图将paypal sandbox与我在asp.net中的项目集成。

重定向到贝宝沙箱工作非常好！您可以查看您的购物车！你可以付款！但问题是当贝宝设置重定向到我的Success.aspx页面！

我得到的错误是

A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 192.168.0.101:808

我正在使用流写入程序Object！

等等，让我发布我的代码！

这是Success.aspx 的page_load偶数

   protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                // Used parts from https://www.paypaltech.com/PDTGen/
                // Visit above URL to auto-generate PDT script
                authToken = WebConfigurationManager.AppSettings["PDTToken"];
                //read in txn token from querystring
                txToken = Request.QueryString.Get("tx");

                query = string.Format("cmd=_notify-synch&tx={0}&at={1}", txToken, authToken);
                // Create the request back
                string url = WebConfigurationManager.AppSettings["PayPalSubmitUrl"];
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
                // Set values for the request back
                req.Method = "POST";
                req.ContentType = "application/x-www-form-urlencoded";
                req.ContentLength = query.Length;
                // Write the request back IPN strings
                StreamWriter stOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
                stOut.Write(query);
                stOut.Close();
                // Do the request to PayPal and get the response
                StreamReader stIn = new StreamReader(req.GetResponse().GetResponseStream());
                strResponse = stIn.ReadToEnd();
                stIn.Close();
                // sanity check
                Label2.Text = strResponse;
                // If response was SUCCESS, parse response string and output details
                if (strResponse.StartsWith("SUCCESS"))
                {
                    PDTHolder pdt = PDTHolder.Parse(strResponse);
                    Label1.Text = string.Format("Thank you {0} {1} [{2}] for your payment of {3} {4}!",
                        pdt.PayerFirstName, pdt.PayerLastName, pdt.PayerEmail, pdt.GrossTotal, pdt.Currency);
                }
                else
                {
                    Label1.Text = "Oooops, something went wrong...";
                }
            }
        }

这句话制造了错误！！

StreamWriter stOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);

发生此类异常

    Exception Details: System.Net.Sockets.SocketException:
 A connection attempt failed because the connected party did
 not properly respond after a period of time, 
or established connection failed because connected
 host has failed to respond 192.168.0.101:808