Запрос к сайту и ошибка "something wrong" - C#

public static string Post(string login, string otvet)
        {
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://moonbit.co.in/");
 
            req.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.118 Safari/537.36";
            req.Host = "moonbit.co.in";
            req.Headers.Add("Origin: http://moonbit.co.in");
            //req.KeepAlive = true;
            req.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
            req.Method = "POST";
            req.CookieContainer = new CookieContainer();
            req.KeepAlive = true;
            //req.Headers.Add("Cache-Control: max-age=0");
            req.ContentType = "application/x-www-form-urlencoded";
            req.Referer = "http://moonbit.co.in/";
            //req.Headers.Add("Accept-Language: ru-RU,ru;q=0.8,en-US;q=0.6,en;q=0.4");
            //req.Headers.Add("Accept-Encoding: gzip, deflate");
 
            req.CookieContainer = new CookieContainer();
            req.CookieContainer.Add(new Cookie("user", "PaymentAddress=" + login) { Domain = "moonbit.co.in"});

            //=================
            string data = Get("http://moonbit.co.in", "moonbit.co.in", false, false, false, false);
            string __VIEWSTATE = Parse(data, "id=\"__VIEWSTATE\" value=\"", "\"/>");
            string __VIEWSTATEGENERATOR = Parse(data, "id=\"__VIEWSTATEGENERATOR\" value=\"", "\"/>");
            string __EVENTVALIDATION = Parse(data, "id=\"__EVENTVALIDATION\" value=\"", "\"/>");
            //=================
 
            string postData = "__EVENTTARGET=&__EVENTARGUMENT=&" +
                              "__VIEWSTATE=" + __VIEWSTATE + "&" +
                              "__VIEWSTATEGENERATOR=" + __VIEWSTATEGENERATOR + "&" +
                              "__EVENTVALIDATION=" + __EVENTVALIDATION + "&" +
                              "AB=false&" +
                              "adcopy_response=" + otvet + "&" +
                              "adcopy_challenge=" + challange + "&" +
                              "ctl00$PagePopupPlaceholder$ClaimButton=submit&" +
                              "ctl00$PagePopupPlaceholder$ClaimReadyAlertOption=on&" +
                              "ctl00$PagePopupPlaceholder$ClaimAmountAlertValue=500&" +
                              "ctl00$PagePopupPlaceholder$PageTitleAlertOption=on&" +
                              "ctl00$PagePopupPlaceholder$PlaySoundAlertOption=on";
                            
            //Encoding encoding = Encoding.UTF8;
            byte[] byte1 = System.Text.Encoding.ASCII.GetBytes(postData); 
            req.ContentLength = byte1.Length;
            Stream st=req.GetRequestStream();
            st.Write(byte1, 0, byte1.Length);
            st.Close();
 
            using (HttpWebResponse httpWebResponse = (HttpWebResponse)req.GetResponse())
            { 
                using(StreamReader reader = new StreamReader(httpWebResponse.GetResponseStream())){
                    return reader.ReadLine();   
                }
            }

        }