private void button1_Click(object sender, EventArgs e)
        {
            IPEndPoint ip = new IPEndPoint(Dns.GetHostEntry(Dns.GetHostName()).AddressList[0], 8001);
            Socket sk = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            sk.Bind(ip);
            sk.Listen(1024);
            Socket ac = sk.Accept();
            byte[] by = new byte[1024];
            int sum = ac.Receive(by);
            IPEndPoint ip2 = (IPEndPoint)ac.RemoteEndPoint;
            listBox1.Items.Add("来自" + ip2.Address + "对你说");
            listBox1.Items.Add(Convert.ToSingle(sum));
            ac.Close();
            sk.Close();
        }
这是服务端程序的代码，当我点击按钮时，程序死机啦，没办法我改了下端口，把8001成别的了，程序又说，通常每个套接字地址(协议/网络地址/端口)只允许使用一次。这到底是怎么回事啊，帮帮忙哈

大哥们看了能帮忙解决一下吗