TCP传输和线程问题

thread = new Thread(new ThreadStart(StartUp));
Thread.Sleep(100);
thread.Start(); 
              ----------------------------窗体加载时执行的线程 用来监听链接的客户端.
 public void StartUp()
        {
            IPAddress _ip = Dns.GetHostAddresses(Dns.GetHostName())[0];
            _tcpl = new TcpListener(_ip, _port);
            _tcpl.Start();
            while (true)
            {
                byte[] packetBuff = new byte[_maxPacket];
                Socket newClient = _tcpl.AcceptSocket();
                newClient.Receive(packetBuff);
                string UserName = Encoding.Unicode.GetString(packetBuff).TrimEnd('\0');
                if (_transmit_tb.Count != 0 && _transmit_tb.ContainsKey(UserName))
                {
                    newClient.Send(Encoding.Unicode.GetBytes("cmd::Failed"));//返回值 已存在的用户名
                }
                else
                {
                    newClient.Send(Encoding.Unicode.GetBytes("cmd::Successful"));// 添加成功
                }
                //将新连接加入转发表并创建线程为其服务
                Form.CheckForIllegalCrossThreadCalls = false;
                _transmit_tb.Add(UserName, newClient);
                lbServer.Items.Add(UserName);
            }
        } 
------------------------------------------------点击按钮后执行的线程程序。
foreach (DictionaryEntry de in _transmit_tb)
{
   string _clientName = de.Key as string;
   Socket _clientSkt = de.Value as Socket;
   _clientSkt.Send(Encoding.Unicode.GetBytes("cmd:begin"));
}cliThread = new Thread(new ThreadStart(StartImage));
Thread.Sleep(100);
cliThread.Start(); 
--------------------------------------------------线程程序
 public void StartImage()
 {
   for (int i = 0; i < lbServer.Items.Count; i++)  //循环遍历ListBox中的地址
   {
       string userName = lbServer.Items[i].ToString();
       clientThread = new Thread(new ParameterizedThreadStart(ThreadFunc));
       clientThread.Start(userName);-----将地址传输到下一个方法中。
   }
 }     
-----------------------------------------------------------执行线程发送客户端
private void ThreadFunc(object obj)
{
            //通过转发表得到当前用户套接字
    Socket clientSkt = _transmit_tb[obj] as Socket;
    while (true)
    {
      try
      {
          byte[] _cmdBuff = new byte[128];
          clientSkt.Receive(_cmdBuff);
          string _cmd = DecodingBytes(_cmdBuff);
          /// "01"-离线
          /// "02"-请求在线列表
          /// "03"-请求发送图片
          switch (_cmd)
          {
             case "01":
                {
                    _transmit_tb.Remove(obj);
                    string svrlog = string.Format("[系统消息]用户 {0} 在 {1} 已断开... 当前在线人数: {2}\r\n\r\n", obj, DateTime.Now, _transmit_tb.Count);
                    MessageBox.Show(svrlog, "用户退出", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    Thread.CurrentThread.Abort();
                    break;
                 }
             case "02":
                 {
                    byte[] onlineBuff = SerializeOnlineList();
                    //先发送响应信号，用于客户机的判断，"11"表示服务发给客户机的更新在线列表的命令
                    clientSkt.Send(new byte[] { 1, 1 });
                    clientSkt.Send(onlineBuff);
                    break;
                  }
              case "03":
                  {
                    byte[] _msgBuff = InterceptClass.GetDesktopBitmapBytes();//发送图片数组clientSkt.Send(_msgBuff);
                    foreach (DictionaryEntry de in _transmit_tb)
                    {
                       string _clientName = de.Key as string;
                       Socket _clientSkt = de.Value as Socket;
                       if (_clientName.Equals(obj))
                        {
                           _clientSkt.Send(_msgBuff);
                         }
                     }
                        break;
                   }
                }
               catch (SocketException)
              {
                    _transmit_tb.Remove(obj);
                    Thread.CurrentThread.Abort();
              }
            }
        ---------------------------------------------
我的程序是在截取 桌面的屏幕 发送到客户端中   现在 存在的问题是  当我鼠标在服务器端不停运动  程序还不短执行
如果 静止不动 一会 就不在截取屏幕了  是不是我的线程哪里出了问题？
第二个问题就是  当 我程序开始 截屏发送的时候  在登录一个客户端 就会出错 希望各位 给指点下  谢谢啦！~