System.Net.Web exception in request.GetRequestStream()

///Authored by-: Sambeet Panigrahi
///Dated on-:10th January 2015

/*This program updates the Netduino Plus switch state to Thingspeak*/
using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;
using SecretLabs.NETMF.Hardware;
using SecretLabs.NETMF.Hardware.Netduino;
using System.Text;
using System.IO;


namespace LED__control_Thingspeak
{
    public class Program
    {
        public static void Main()
        {
            var SwitchPort = new InputPort(Pins.ONBOARD_BTN, false, Port.ResistorMode.
                Disabled);                                                           //Open the switchport

            bool onned = SwitchPort.Read();//Read the status of switchport

            if (onned)
            {
                update_thingspeak("30");
            }
            else
            {
                update_thingspeak("60");
            }

        }//Main ends

        static void update_thingspeak(string value)
        {
            //Create a http response object
                WebRequest request = HttpWebRequest.Create("https://api.thingspeak.com/update");
            //Setting the request method
                request.Method = "POST";
            //The data to be sent
                string data = "api_key=" + "T5Q1Y9QBY1TULCBG" + "&field1=" + value;
            //Creating the byte array
                byte[] bytearray = Encoding.UTF8.GetBytes(data);
            //Setting the MIME
                request.ContentType = "application/x-www-form-urlencoded";
                request.ContentLength = bytearray.Length;
            //Opening the datastream
                Stream datastream = request.GetRequestStream();
            //Writing to the datastream
                datastream.Write(bytearray, 0, bytearray.Length);
            //Closing the stream
                datastream.Close();
            

            //Obtaining a response
                WebResponse response = request.GetResponse();//Creating a response
                datastream = response.GetResponseStream();//Getting the response stream
                StreamReader reader = new StreamReader(datastream);// Read the content.
                string responseFromServer = reader.ReadToEnd();// Display the content.
                Debug.Print(responseFromServer);
            
        }//update_thingspeak ends
    }//class program ends
}//namespace ends