偶尔遇到的“The request was aborted:Could not create SSL/TLS secure channel.”怎么解决？

if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))///https请求

{

    ServicePointManager.Expect100Continue = true;

    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls; //SSL3协议替换成TLS协议

    ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);

    webRequest = WebRequest.Create(url) as HttpWebRequest;

    webRequest.ProtocolVersion = HttpVersion.Version10;

}

else

{

    webRequest = WebRequest.Create(url) as HttpWebRequest;

}