here is my code

        Socket sck = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        sck.Bind(new IPEndPoint(IPAddress.Any, 0));

        // Broadcast to find server
        string msg = "Imlookingforaserver:" + udp_listen_port;
        byte[] sendBytes4 = Encoding.ASCII.GetBytes(msg);
        IPEndPoint groupEP = new IPEndPoint(IPAddress.Parse("255.255.255.255"), server_port);
        sck.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, 1);
        sck.SendTo(sendBytes4, groupEP);

        //Wait response from server
        Socket sck2 = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        sck2.Bind(new IPEndPoint(IPAddress.Any, udp_listen_port));
        byte[] buffer = new byte[128];
        EndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, udp_listen_port);
        sck2.ReceiveFrom(buffer, ref remoteEndPoint); //<<< I never pass this line

I use above code to try find a server. First i broadcast a message and then i wait response from server.

A test i made with the server written in c++ and running in windows vista, client written in C# and run on the same machine with server.

Problem is: The server can receive message which client broadcast. But client can not receive anything from server.

I try to write a client with c++ and it work like a charm, i think my problem is in C# client.