How do I get my program.cs to delete an external file when a form is closed?

Andy,
First of all sorry for rushing off yest. After I posted my reply to you in a hurry I had to rush to catch a bus and couldnt login thereafter. I looked at all the replies so far and also your new error. I recreated your entire app at my end and tested it. With some tweaking, it's working fine.  You dont need to include System.IO while using FileInfo becauase you have already written a using statement for the namespace at the top:
using System.IO;
As for the other modification I made it was wrt reader.Close(). It needs to be placed right after you finish reading the file.
See the final code below, it's working smoothly without any hitch and the file gets deleted too.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.IO.Ports;
using System.Threading;
namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
        SerialPort sp = new SerialPort();
        string input = "";
        public Form1()
        {
            InitializeComponent();
            this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.Form1_FormClosing);
            string s = System.Environment.CurrentDirectory + "\\Email.txt";
            MessageBox.Show(s);
        }
        //
        //
        //Code in here to send message out
        //
        private void Form1_Load(object sender, EventArgs e)
        {
            lblStatus.Text = "";
            cmbRecipient.DropDownStyle = ComboBoxStyle.DropDownList;
            cmbBoxPorts.DropDownStyle = ComboBoxStyle.DropDownList;
            string[] ports = SerialPort.GetPortNames();
            foreach (string port in ports)
            {
                cmbBoxPorts.Items.Add(port);
            }
            try
            {
                cmbBoxPorts.SelectedIndex = 0;
            }
            catch { }
            try
            {
                DataTable table = new DataTable();
                DataColumn colEmail = new DataColumn("Email");
                DataColumn colRecipient = new DataColumn("Recipient");
                table.Columns.Add(colEmail);
                table.Columns.Add(colRecipient);
                StreamReader reader = new StreamReader(System.Environment.CurrentDirectory + "\\Email.txt");
               
                do
                {
                    Console.WriteLine(reader.ReadLine().Split(','));
                    table.Rows.Add(reader.ReadLine().Split(','));
                }
                while (reader.Peek() != -1);
               
                // Close the reader here
                reader.Close();
                cmbRecipient.DataSource = table;
                cmbRecipient.DisplayMember = "Email";
                cmbRecipient.ValueMember = "Recipient";
                cmbRecipient.SelectedIndex = 0;
            }
            catch
            {
                MessageBox.Show("ERROR: Unable to read txt file.\r\nCreate a 'Email.txt' file in the following format...\r\n\r\n,Please /Select Recipient\r\[email protected],Andy R\r\[email protected],Brian N");
              
            }
        }
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            FileInfo fidel = new FileInfo("Email.txt");
            fidel.Delete();
        }

        private void linkLabel1_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            MessageBox.Show("Version 1.0\r\nE-mailer.");
        }
    }
}