Problem in Sending Sms in c# pdu mode

{
        int port;
        int baud;
        string status, acknowlegde;
        GsmCommMain myport;
        public Form1()
        {
            InitializeComponent();
        }
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
        }
        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                port = int.Parse(cmbport.Text);
                baud = int.Parse(cmbbaud.Text);
                myport = new GsmCommMain(port, baud);
                myport.Open();
                if (myport.IsConnected())
                {
                    status = "Connected";
                    lblstatus.Text = status;
                }
                else
                {
                    status = "Not connected";
                    lblstatus.Text = status;
                }
                myport.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
                MessageBox.Show("Invalid Connection Setting");
                status = "Not Connected";
                lblstatus.Text = status;
            }
        }
        public void showack(string acknowlegde)
        {
            lsthistory.Items.Add(acknowlegde);
            lsthistory.Items.Add("Recipent::" + lsthistory.Text + "\n");
            lsthistory.Items.Add("Message:\n");
            lsthistory.Items.Add(txtmsg.Text);
            lsthistory.Items.Add("-------------------------\n");
        }
        private void button1_Click_1(object sender, EventArgs e)
        {
            try
            {
                if (status == "Connected")
                {
                    SmsSubmitPdu pdu = new SmsSubmitPdu(txtmsg.Text, lsthistory.Text);
                    myport.Open();
                    myport.SendMessage(pdu);
                    Cursor.Current = Cursors.WaitCursor;
                    myport.Close();
                    acknowlegde = "Message Sent Sucessfuly!";
                    showack(acknowlegde);
                }
                else
                {
                    acknowlegde = "Message not sent! Retry?";
                    showack(acknowlegde);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }