System.Net.WebException: 远程服务器返回错误: (611) Biz Error

Question

代码如下：
internal static string doGet(string Url)
        {
            string retString = null;
            try
            {
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
                request.Method = "GET";
                request.ContentType = "text/html;charset=UTF-8";
                request.Timeout = 30000;
                request.ReadWriteTimeout = 30000;
                using (WebResponse response = request.GetResponse())
                {
                    Stream myResponseStream = response.GetResponseStream();
                    StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
                    retString = myStreamReader.ReadToEnd();
                    myStreamReader.Close();
                    myResponseStream.Close();
                }
            }
            catch (System.Exception ex)
            {
                WriteErrLog(ex.ToString());
            }            return retString;
        }