При подключении второго клиента к серверу возникает ошибка "IAsyncResult не был получен" - C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
 
namespace Chat
{
    public partial class Form1 : Form
    {
        Socket _serverSocket, _clientSocket;
        List<Socket> listSockets= new List<Socket>();
        List<string> listNicks = new List<string>();
        private byte[] _buffer;
        string path= @"C:\Users\haker_000\Documents\visual studio 2012\Projects\Chat\Client\bin\Debug\Client.exe";
        private byte[] _buffernick;
        bool enable = false;
 
        public Form1()
        {
            InitializeComponent();
            Process.Start(path);
        }

        private void StartServer()
        {
            try
            {
                _serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                _serverSocket.Bind(new IPEndPoint(IPAddress.Any, 3333));
                _serverSocket.Listen(0);
                _serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
                enable = true;
                button3.Enabled = false;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK);
            }
        }
 
        private void AcceptCallback(IAsyncResult ar)
        {
            try
            {
 
                _clientSocket = _serverSocket.EndAccept(ar);
                listSockets.Add(_clientSocket);
                _buffer = new byte[_clientSocket.ReceiveBufferSize];
                _buffernick = new byte[_clientSocket.ReceiveBufferSize];
                _clientSocket.BeginReceive(_buffernick, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveNickCallback), null);
                _clientSocket.BeginReceive(_buffer, 0, _buffer.Length,SocketFlags.None, new AsyncCallback(ReceiveCallback),null);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK);
            }
        }
 
        private void ReceiveNickCallback(IAsyncResult ar)
        {
            try
            {
                _clientSocket.EndReceive(ar);
                string nick = Encoding.Unicode.GetString(_buffernick);
                listNicks.Add(nick);
                textBox3.AppendText("\r\n" + nick);
                AppendNickToTextBox(nick);
                SentToAllClients(nick);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK);
            }
        }
 
        private void AppendNickToTextBox(string text)
        {
            MethodInvoker invoker = new MethodInvoker(delegate
            {
                textBox2.Text += "\r\n"+ "Welcome " + text;
            });
            this.Invoke(invoker);
        }
 
        private void ReceiveCallback(IAsyncResult ar)
        {
            try
            {
                int received = _clientSocket.EndReceive(ar);
                Array.Resize(ref _buffer, received);
                string text = Encoding.Unicode.GetString(_buffer);
                 AppendToTextBox(text);
                Array.Resize(ref _buffer, _clientSocket.ReceiveBufferSize);
                _clientSocket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
                SentToAllClients(text);
                
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK);
            }
        }
 
        private void SentToAllClients(string text)
        {
            byte[] _sendText = Encoding.Unicode.GetBytes(text);
            for (int i = 0; i < listSockets.Count; i++)
            {
                try
                {
                    listSockets[i].BeginSend(_sendText, 0, _sendText.Length, SocketFlags.None, new AsyncCallback(SendnickCallback), null);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK);
                }
            }
 
        }
 
        private void SendnickCallback(IAsyncResult ar)
        {
            try
            {
                _clientSocket.EndSend(ar);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
 
        private void AppendToTextBox(string text)
        {
            MethodInvoker invoker = new MethodInvoker(delegate
                {
                    textBox2.Text += "\r\n" + text;
                });
            this.Invoke(invoker);
        }
 
        private void button3_Click(object sender, EventArgs e)
        {
            StartServer();
        }
 
        private void timer1_Tick(object sender, EventArgs e)
        {
            if (enable == true)
            {
                _serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
            }
        }

    }
}