Could not create SSL/TLS secure channel

I get this error for a specific website, that they announced they made some changes a couple months ago. Now when I check it through c#.... something is not right. The other websites I check are working allright with this code.
Can someone elucidate it for me, please?

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

I am using this code:

// I google it and find this 3lines as being helpful - THEY ARE NOT HELPING AT ALL
            ServicePointManager.Expect100Continue = true;
            ServicePointManager.DefaultConnectionLimit = 9999;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls; 
//(In my VS2010, I only see Ssl3 and Tls,that's it - this may be the cause?)

            HttpWebRequest request;
            HttpWebResponse response = null;
            Stream stream = null;
            request = (HttpWebRequest)WebRequest.Create("https://www.MyWebsiteToCheck.com/");
            request.UserAgent = "Foo";
            request.Accept = "*/*";

            request.UseDefaultCredentials = true;
            request.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;

//{"The request was aborted: Could not create SSL/TLS secure channel."}
//and response is null.
            response = (HttpWebResponse)request.GetResponse();//<<<here it breakes
            stream = response.GetResponseStream();

            if (stream != null) stream.Close();
            if (response != null) response.Close();

Thank you.

What I have tried:

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Tags: C#