Trouble using spamd in Ubuntu under VMWare

using System;
using System.Net;
using System.Text;
using System.Windows.Forms;
 
namespace SATest
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            try
            {
                textBox1.Text += "Preparing data...\r\n";
 
                StringBuilder SB = new StringBuilder();
 
                SB.Append("PROCESS SPAMC/1.0");
                SB.Append("\r\nSubject: Test spam mail (GTUBE)");
                SB.Append("\r\nMessage-ID: <gtube1.1010101@example.net>");
                SB.Append("\r\nDate: Wed, 23 Jul 2003 23:30:00 +0200");
                SB.Append("\r\nFrom: Sender <sender@example.net>");
                SB.Append("\r\nTo: Recipient <recipient@example.net>");
                SB.Append("\r\nPrecedence: junk");
                SB.Append("\r\nMIME-Version: 1.0");
                SB.Append("\r\nContent-Type: text/plain; charset=us-ascii");
                SB.Append("\r\nContent-Transfer-Encoding: 7bit");
                SB.Append("\r\n");
                SB.Append("\r\nIf your spam filter supports it, the GTUBE " + 
                          "provides a test by which you");
                SB.Append("\r\ncan verify that the filter is installed " + 
                          "correctly and is detecting incoming");
                SB.Append("\r\nspam. You can send yourself a test mail " + 
                          "containing the following string of");
                SB.Append("\r\ncharacters (in upper case and with no white " +
                          "spaces and line breaks):");
                SB.Append("\r\n");
                SB.Append("\r\nXJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-" + 
                          "ANTI-UBE-TEST-EMAIL*C.34X");
                SB.Append("\r\n");
                SB.Append("\r\nYou should send this test mail from an " + 
                          "account outside of your network.");
                SB.Append("\r\n");
 
                Byte[] buffer = Encoding.ASCII.GetBytes(SB.ToString());
 
                textBox1.Text += "Sending data...\r\n";
 
                System.Net.Sockets.Socket socket = 
                    new System.Net.Sockets.Socket(
                        System.Net.Sockets.AddressFamily.InterNetwork,
                        System.Net.Sockets.SocketType.Stream,
                        System.Net.Sockets.ProtocolType.Tcp);
                IPEndPoint ipe = 
                    new IPEndPoint(IPAddress.Parse("192.168.31.128"), 783);
 
                //This is the line on which the error occurs:
                socket.Connect(ipe);
                socket.Send(buffer);
                socket.Shutdown(System.Net.Sockets.SocketShutdown.Send);
 
                textBox1.Text += "Receiving data\r\n";
 
                Int32 r;
 
                do
                {
                    Byte[] recbuf = new Byte[1024];
                    r = socket.Receive(recbuf);
                    textBox1.Text += Encoding.ASCII.GetString(recbuf, 0, r);
                }
                while (r != 0);
 
                textBox1.Text += "OK\r\n";
            }
            catch (Exception ex)
            {
                textBox1.Text += "\r\n" + ex.ToString() + "\r\n";
            }
        }
    }
}