مشکل کد کپچا

[malihe joon]

protected void Page_Load(object sender, EventArgs e)
{


string ABC = "QWERTYUIOPASDFGHJKLZXCVBNM1234567890qwertyuiopasdf ghjklzxcvbnm";

Random rand = new Random();

object ABC1 = rand.Next(1, 62);
object ABC2 = rand.Next(1, 62);
object ABC3 = rand.Next(1, 62);
object ABC4 = rand.Next(1, 62);
object ABC5 = rand.Next(1, 62);
object ABC6 = rand.Next(1, 62);

string strABC1 = ABC.Substring(Convert.ToInt32(ABC1), 1);
string strABC2 = ABC.Substring(Convert.ToInt32(ABC2), 1);
string strABC3 = ABC.Substring(Convert.ToInt32(ABC3), 1);
string strABC4 = ABC.Substring(Convert.ToInt32(ABC4), 1);
string strABC5 = ABC.Substring(Convert.ToInt32(ABC5), 1);
string strABC6 = ABC.Substring(Convert.ToInt32(ABC6), 1);

string result = strABC1 + strABC2 + strABC3 + strABC4 + strABC5 + strABC6;


Session.Add("result", result);


Bitmap SecImage = new Bitmap(Server.MapPath("~/image/capcha-1.jpg"));
Graphics Grapimage = Graphics.FromImage(SecImage);
Grapimage.DrawString(result.ToString(), new Font("Tohoma", 12, FontStyle.Strikeout), SystemBrushes.WindowText, new PointF());
SecImage.Save(Server.MapPath("~/image/security capcha-1.jpg"));

Image1.ImageUrl = "~/image/security capcha-1.jpg";


}
protected void Button1_Click(object sender, EventArgs e)
{

Response.Redirect("Default4.aspx");

}
protected void Button2_Click(object sender, EventArgs e)
{
string result = (string)Session["result"];
if (TextBox1.Text == result)
{

if (TextBox2.Text == "ali" && TextBox3.Text == "123")
{
{
Response.Redirect("Default.aspx");
}
}
}
else
{
Label1.Text = "jsjhshh";
}
}