创建验证码的时候，为什么其他的控件不显示了？

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;

public partial class _2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        this.CreateCheckCodeImage(GenerateCheckCode());

    }
     #region Web 窗体设计器生成的代码
    override protected void OnInit(EventArgs e)
    {
        //
        // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
        //
        InitializeComponent();
        base.OnInit(e);
    }

    /// <summary>
    /// 设计器支持所需的方法 - 不要使用代码编辑器修改
    /// 此方法的内容。
    /// </summary>
    private void InitializeComponent()
    {
        this.Load += new System.EventHandler(this.Page_Load);
    }
    #endregion

    private string GenerateCheckCode()
    {
        int number;
        char code;
        string checkCode = String.Empty;

        System.Random random = new Random();

        for (int i = 0; i < 5; i++)
        {
            number = random.Next();

            if (number % 2 == 0)
                code = (char)('0' + (char)(number % 10));
            else
                code = (char)('A' + (char)(number % 26));

            checkCode += code.ToString();
        }

      //  Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

        Session.Add("CheckCode", checkCode);

        return checkCode;
    }

    private void CreateCheckCodeImage(string checkCode)
    {

        if (checkCode == null || checkCode.Trim() == String.Empty)
            return;

        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
       Graphics g = Graphics.FromImage(image);

        try
        {
            //生成随机生成器
            Random random = new Random();

            //清空图片背景色
            g.Clear(Color.White);

            //画图片的背景噪音线
            for (int i = 0; i < 25; i++)
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);

                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }

            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);

            //画图片的前景噪音点
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);

                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //画图片的边框线
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
    protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (Request.Cookies["CheckCode"] == null)
        {
            lblMessage.Text = "aaaaaaa";
            lblMessage.Visible = true;
            return;
        }
        if (String.Compare(Request.Cookies["CheckCode"].Value, txtCheckCode.Text, true) != 0)
        {
            lblMessage.Text = "bbbbbbbbb";
            lblMessage.Visible = true;
            return;
        }
    } --------------------编程问答-------------------- 谢谢！

补充：.NET技术 ,  ASP.NET