Delegates asychronous callbacks - textbox control does not get updated

I am trying to use delegates to make asynchronous calls with callbacks.
The below code works EXCEPT that TextBox2.Text does not get updated.  Why?
I am no expert... must be something stupid I am doing... please help.  A
Here is the code behind... the asp page just have 2 text boxes.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Contexts;
using System.Runtime.Remoting.Messaging;

public partial class Default : System.Web.UI.Page
{
    delegate int MyDelegate(int iCallTime);
    protected void Page_Load(object sender, EventArgs e)
    {
        MyDelegate dlgt = new MyDelegate(this.LongRunningMethod);
     &nb ...