How can I solve this C# programming problem ?

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C#

WinForms

I have a small server which is receive and send the message back to the client.
this is the client side
when i open the client it will connect to server through Connect()

public Form1()
        {
            InitializeComponent();
            Connect();
            CheckForIllegalCrossThreadCalls = false;
        }

this is my connect

void Connect()
        {
            ipep = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 9999);
            server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            try
            {
                server.Connect(ipep);
            }
            catch (SocketException e)
            {
                MessageBox.Show(Convert.ToString(e));           
            }
            Thread listen = new Thread(Receive);
            listen.IsBackground = true; ;
            listen.Start();
        }

and i have a receive like this

void Receive()
        {
            datarec = new byte[1024];
            try
            {
                while (true)
                {
                    string StringData;
                    rec = server.Receive(datarec);
                    StringData = Encoding.ASCII.GetString(data, 0, rec);
                    txtShow.Text = StringData;
                }
            }
            catch
            {
                Close();
            }
        }

and i send data through a button have Send method

void Send(string s)
        {
            data = new byte[1024];
            data = Encoding.ASCII.GetBytes(s);
            server.Send(data, data.Length, SocketFlags.None);
            
        }

this is the server side
i have a thread server

public static void Process(Socket client)
        {
            byte[] data = new byte[1024];
            int recv;
            string dataInput;
            IPEndPoint clientep = (IPEndPoint)client.RemoteEndPoint;
            Console.WriteLine("Connected with {0} at port {1}", clientep.Address, clientep.Port);             
            
            while (true)
            {
                try
                {                   
                     recv = client.Receive(data);
                    dataInput = Encoding.ASCII.GetString(data, 0, recv);
                    Console.WriteLine(dataInput);
                    client.Send(data);
                }
                catch (SocketException e)
                {

                    Console.WriteLine(e);
                }
            }
        }

the server receive message but when it send message back it has an error "An existing connection was forcibly closed by the remote host"
Can you guys tell me where i was wrong and how can i fix it?
Sorry for missing the Send Button. Here is it

private void button1_Click(object sender, EventArgs e)
        {
            string s = txtText.Text;
            Send(s);          
        }

What I have tried:

I have searching this error for 2 days but still not understand how to fix it. Can you guys tell me or give me a source where i can find how to fix it ? thanks so much