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

Question

It was working well before a week but now it shows following error. I have tried the following things but of no use.

ServicePointManager.Expect100Continue = true;
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;

so suggest me with possible solution

public string HttpCall(string NvpRequest) //CallNvpServer
    {
        string url = pendpointurl;

        //To Add the credentials from the profile
        string strPost = NvpRequest + "&" + buildCredentialsNVPString();
        strPost = strPost + "&BUTTONSOURCE=" + HttpUtility.UrlEncode(BNCode);

        ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
        // allows for validation of SSL conversations
        ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };


        HttpWebRequest objRequest = (HttpWebRequest)WebRequest.Create(url);
        objRequest.Timeout = Timeout;
        objRequest.Method = "POST";
        objRequest.ContentLength = strPost.Length;

        try
        {
            using (StreamWriter myWriter = new StreamWriter(objRequest.GetRequestStream()))
            {
                myWriter.Write(strPost);
            }
        }
        catch (Exception e)
        {
            /*
            if (log.IsFatalEnabled)
            {
                log.Fatal(e.Message, this);
            }*/
        }

        //Retrieve the Response returned from the NVP API call to PayPal
        HttpWebResponse objResponse = (HttpWebResponse)objRequest.GetResponse();
        string result;
        using (StreamReader sr = new StreamReader(objResponse.GetResponseStream()))
        {
            result = sr.ReadToEnd();
        }

        //Logging the response of the transaction
        /* if (log.IsInfoEnabled)
         {
             log.Info("Result :" +
                       " Elapsed Time : " + (DateTime.Now - startDate).Milliseconds + " ms" +
                      result);
         }
         */
        return result;
    }

Answer 1

I just ran into this same problem in my testing environment as well (luckily my live payments are going through). I fixed it by changing:

public PayPalAPI(string specialAccount = "")
{
    System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls;

to

public PayPalAPI(string specialAccount = "")
{
    System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;

They disabled support for SSL3 a while ago: https://www.paypal.com/uk/webapps/mpp/ssl-security-update, specifically stating

Ensure you are connecting to PayPal endpoints using TLS 1.0 or 1.2 (not all API endpoints currently support TLS 1.1).

Their latest update (thx for the comment update from @awesome) states:

PayPal is updating its services to require TLS 1.2 for all HTTPS connections. At this time, PayPal will also require HTTP/1.1 for all connections... To avoid any disruption of service, you must verify that your systems are ready for this change by June 17, 2016