socket编程报错，请教！

            IPAddress ServerIp = GetServerIP();            IPEndPoint iep = new IPEndPoint(ServerIp, 8000);
            socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);            Control.CheckForIllegalCrossThreadCalls = false;            socket.Bind(iep);           socket.Listen(1); // 这句报错。错误如下：System.Net.Sockets.SocketException: The attempted operation is not supported for the type of object referenced
   at System.Net.Sockets.Socket.Listen(Int32 backlog)
   at SOCKET.Form1.ls() in C:\Documents and Settings\daniel\Desktop\c#学习笔记\c#网络编程\SOCKET\SOCKET\Form1.cs:line 63  
 如果
     socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);换成tcp的如下     socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);则不报错，请指教