asp.net-mvc – 请求已中止：无法创建SSL / TLS安全通道.System.

The request was aborted: Could not create SSL/TLS secure channel.

我也使用Paypal的Sandbox帐户进行测试.

它从这一行抛出错误：

var sw = new StreamWriter(req.GetRequestStream()

这是下面的代码：

var req = (HttpWebRequest)WebRequest.Create(GetPaypalUrl());
        req.Method = "POST";
        req.ContentType = "application/x-www-form-urlencoded";
        req.ProtocolVersion = HttpVersion.Version10;

        string formContent = string.Format("cmd=_notify-synch&at={0}&tx={1}",_paypalStandardPaymentSettings.PdtToken,tx);
        req.ContentLength = formContent.Length;

        using (var sw = new StreamWriter(req.GetRequestStream(),Encoding.ASCII))
            sw.Write(formContent);