htmlagilitypack解析，异常错误

Question

                using (WebClient wc = new WebClient())
            {
                wc.Headers.Add("user-agent", "Mozilla/5.0 (Windows; Windows NT 5.1; rv:1.9.2.4) Gecko/20100611 Firefox/3.6.4");
                string html = wc.DownloadString("https://www.dividends.sg/view/D05");
                HtmlDocument doc = new HtmlDocument();
                doc.LoadHtml(html);
            }

错误低于

$exception  {System.Net.WebException: Error: SecureChannelFailure (The authentication or decryption has failed.) …} System.Net.WebException

我尝试使用bs4并且当我添加useragent时它工作但我现在切换到c＃并且我不知道这是否是正确的方法。