System.Net.WebException на другом ПК - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO;
using System.Timers;
 
namespace Post
{
    class PostParam
    {
        public string parameter;
        public string value;
 
        public PostParam(string parameter, string value)
        {
            this.parameter = parameter;
            this.value = value;
        }
        public override string ToString()
        {
            return String.Format("{0}={1}", parameter, value);
        }
    }
 
    class PostRequestString : List<PostParam>
    {
        private string RequestString;
 
        public byte[] GetRequestString()
        {
            RequestString += base[0].ToString();
 
            return Encoding.GetEncoding(1251).GetBytes(RequestString);
        }
    }
 
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                System.Timers.Timer myTimer = new System.Timers.Timer(5000);
                myTimer.Elapsed += new System.Timers.ElapsedEventHandler(myTimer_Elapsed);
                myTimer.Start();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadKey();
        }
 
        static void myTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            try
            {
                PostParam PostParam = new PostParam("test", DateTime.Now.TimeOfDay.ToString());
 
                PostRequestString PostParams = new PostRequestString();
                PostParams.Add(PostParam);
 
                byte[] RequestString = PostParams.GetRequestString();
                int RequestStringLength = RequestString.Length;
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(@"http://test.ru/test.php");
                req.Timeout = 3000;
                req.Method = "POST"; // Устанавливаем метод передачи данных в POST
                req.ContentType = "application/x-www-form-urlencoded";
                req.ContentLength = RequestStringLength;
                Stream sendStream = req.GetRequestStream();
                sendStream.Write(RequestString, 0, RequestString.Length);
                sendStream.Close();
                HttpWebResponse res = (HttpWebResponse)req.GetResponse();
                Stream ReceiveStream = res.GetResponseStream();
                StreamReader sr = new StreamReader(ReceiveStream, Encoding.UTF8);
                Console.WriteLine(sr.ReadToEnd());
                Console.WriteLine("Ответ на запрос принят");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally 
            {
                Console.ReadKey();
            }
        }
    }
}