又要来砸分求助高手了，很简单的一段异步代码，哪位高手帮我运行下啊，为什么点完启动点停止就会有那些异常啊
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace AsyncServerWin
{
  public partial class Form1 : Form
  {
  int num = 0;
  EventWaitHandle ewh = new EventWaitHandle(false, EventResetMode.ManualReset);
  TcpListener tl = new TcpListener(IPAddress.Any, 9876);
  public Form1()
  {
  InitializeComponent();
  }

  public void BeginListen()
  {
  try
  {
  tl.Start();
  AsyncCallback ac = new AsyncCallback(MyAcceptTcpClient);
  while (true)
  {
  ewh.Reset();
  tl.BeginAcceptTcpClient(ac, tl);
  ewh.WaitOne();
  }
  }
  catch (Exception ex)
  {
  MessageBox.Show(ex.ToString());
  tl.Stop();
  }
  }
   
  private void button1_Click(object sender, EventArgs e)
  {
  this.button1.Enabled = false;
  Thread t = new Thread(BeginListen);
  t.Start();
   
  }

  public void MyAcceptTcpClient(IAsyncResult ar)
  {
  try
  {
  ewh.Set();
  TcpListener tl = (TcpListener)ar.AsyncState;
  TcpClient tc = tl.EndAcceptTcpClient(ar);
  num++;
  lbConnectionID.Items.Add(((int)tc.Client.Handle).ToString());
  tbNum.Text = num.ToString();
  }
  catch (Exception ex)
  {
  MessageBox.Show(ex.ToString());
  tl.Stop();
  }
  }

  private void button2_Click(object sender, EventArgs e)
  {

  tl.Stop();//---------------------------------------------------这里出问题了！！！
  this.button1.Enabled = true;
  }
  }
}

================================================================================

namespace AsyncServerWin
{
  partial class Form1
  {
  /// <summary>
  /// 必需的设计器变量。
  /// </summary>
  private System.ComponentModel.IContainer components = null;

  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
  protected override void Dispose(bool disposing)
  {
  if (disposing && (components != null))
  {
  components.Dispose();
  }
  base.Dispose(disposing);
  }

  #region Windows 窗体设计器生成的代码

  /// <summary>
  /// 设计器支持所需的方法 - 不要
  /// 使用代码编辑器修改此方法的内容。
  /// &