....
public class MultiContainer : MarshalByRefObject, IMultiContainer
    {
        public string GetClientsList()
        {
            Thread.Sleep(1000);
            return Program.ServerForm.GetClientsList();
        }
....

namespace Client
{
    public partial class Form1 : Form
    {
        Server.IMultiContainer mc;
        private delegate string Delegate();
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            mc = new Server.MultiContainer();
            Delegate del = new Delegate(mc.GetClientsList);
            AsyncCallback callback = new AsyncCallback(Callback);
            del.BeginInvoke(callback, null);
        }
 
        private void Callback(IAsyncResult ar)
        {
            //this callback method is never called...
            Delegate del = (Delegate)((AsyncResult)ar).AsyncDelegate;
            richTextBox1.Text = del.EndInvoke(ar);
        }
...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.Remoting.Messaging;
 
namespace daniweb
{
  public partial class frmAsync : Form
  {
    private delegate string Delegate();
 
    public frmAsync()
    {
      InitializeComponent();
    }
 
    private void button1_Click(object sender, EventArgs e)
    {
      List<string> clients = new List<string>();
      clients.Add("1");
      clients.Add("2");
      clients.Add("3");
      //This is a valid call
 
      new Func<string[], string>(DoWork).BeginInvoke(
        clients.ToArray(),
        new AsyncCallback(CleanupCallback),
        null);
      //This will throw an exception for demonstration purposes
      new Func<string[], string>(DoWork).BeginInvoke(
        default(string[]),
        new AsyncCallback(CleanupCallback),
        null);
    }
 
 
 
    private static string DoWork(string[] clients)
    {
      //clients will be null in one call, resulting in an exception. This is intended
      Console.WriteLine("Work beginning on " + clients.Length.ToString() + " clients.");
      System.Threading.Thread.Sleep(2000);
      return string.Join(", ", clients);
    }
 
    private static void CleanupCallback(IAsyncResult ar)
    {
      AsyncResult result = (AsyncResult)ar;
      Func<string[], string> action = (Func<string[], string>)result.AsyncDelegate;
      try
      {
        string returnValue = action.EndInvoke(ar);
        Console.WriteLine("finished : " + returnValue);
      }
      catch (Exception Ex)
      {
        Console.WriteLine("An error occured: " + Ex.Message);
      }
    }
 
 
  }
}

A first chance exception of type 'System.NullReferenceException' occurred in daniweb.exe
Work beginning on 3 clients.
An error occured: Object reference not set to an instance of an object.
A first chance exception of type 'System.NullReferenceException' occurred in mscorlib.dll
finished : 1, 2, 3

private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                mc = new Server.MultiContainer();
                Delegate del = new Delegate(mc.GetClientsList);
                AsyncCallback callback = new AsyncCallback(Callback);
                del.BeginInvoke(callback, null);
            }
            catch(Exception e1)
            {
               Console.writeline(e1.ToString());
            }
        }

public string GetClientsList()
        {
            try
            {
                Thread.Sleep(1000);
            }
            catch (Exception e1)
            {
                Console.writeline(e1.ToString());
            }
          return Program.ServerForm.GetClientsList();
        }

public string GetClientsList()
        {
            try
            {
                Thread.Sleep(1000);
            }
            catch (Exception e1)
            {
                Console.writeline(e1.ToString());
            }
          return Program.ServerForm.GetClientsList();
        }

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.Remoting.Messaging;
using System.Text;
using System.Windows.Forms;
 
namespace RemoteAsyncTest
{
  public partial class Form1 : Form
  {
    private delegate string Delegate();
    Server.IMultiContainer mc;
 
    public Form1()
    {
      InitializeComponent();
    }
 
    private void button1_Click(object sender, EventArgs e)
    {
      mc = new Server.MultiContainer();
      new Delegate(mc.GetClientsList).BeginInvoke(new AsyncCallback(Callback), null);
    }
 
    private void Callback(IAsyncResult ar)
    {
      System.Diagnostics.Debugger.Break(); //proves it is called
      Delegate del = (Delegate)((AsyncResult)ar).AsyncDelegate;
      string s = del.EndInvoke(ar);
      richTextBox1.Invoke(new MethodInvoker(
        delegate()
        {
          richTextBox1.Text = s;
        }
        ));
    }
  }
}