C# Why doesn't “Flush” force the bytes down the network stream?

I have a project where I'm trying to send a serialized object to the server, then wait for an "OK" or "ERROR" message to come back.

I seem to be having a similar problem to th poster of : TcpClient send/close problem

The issue is that the only way I seem to be able to send the original object is to close the connection, but then (of course) I can't wait to see if the object was processed successfully by the server.

private void button4_Click(object sender, EventArgs e)
{
    RequestPacket req = new RequestPacket();

    /// ... Fill out request packet ...

    /// Connect to the SERVER to send the message...
    TcpClient Client = new TcpClient("localhost", 10287);
    using (NetworkStream ns = Client.GetStream())
    {
        XmlSerializer xml = new XmlSerializer(typeof(RequestPacket));
        xml.Serialize(ns, req);

        /// NOTE: This doesn't seem to do anything.... 
        ///       The server doesn't get the object I just serialized.
        ///       However, if I use ns.Close() it does... 
        ///          but then I can't get the response.
        ns.Flush();

        // Get the response. It should be "OK".
        ResponsePacket resp;

        XmlSerializer xml2 = new XmlSerializer(typeof(ResponsePacket));
        resp = (ResponsePacket)xml2.Deserialize(ns);


        /// ... EVALUATE RESPONSE ...
    }

    Client.Close()
}

UPDATE: In response to one commenter, I don't think the client can be at fault. It is simply waiting for the object, and the object never comes until I close the socket.... however, if I'm wrong, I'll GLADLY eat crow publicly. =) Here's the client:

    static void Main(string[] args)
    {
        // Read the port from the command line, use 10287 for default
        CMD cmd = new CMD(args);
        int port = 10287;

        if (cmd.ContainsKey("p")) port = Convert.ToInt32(cmd["p"]);

        TcpListener l = new TcpListener(port);
        l.Start();

        while (true)
        {
            // Wait for a socket connection.
            TcpClient c = l.AcceptTcpClient();

            Thread T = new Thread(ProcessSocket);

            T.Start(c);
        }
    }


    static void ProcessSocket(object c)
    {
        TcpClient C = (TcpClient)c;

        try
        {
            RequestPacket rp;
            //// Handle the request here.
            using (NetworkStream ns = C.GetStream())
            {
                XmlSerializer xml = new XmlSerializer(typeof(RequestPacket));
                rp = (RequestPacket)xml.Deserialize(ns);
            }

            ProcessPacket(rp);
        }
        catch
        {
            // not much to do except ignore it and go on.
        }
    }

Yeah.... it's that simple.