CaptchaImageText always Null in code to compare with User Input ASP.Net 4.03

The Captcha image is generated in an CImage.aspx.cs . 

So I am trying to compare the Captcha image with the input from the User, but it never gets into the code if the (Session["CaptchaImageText'] != null).
I am able to see the user input via the var see = txtimgcode.Text;  I must be missing something.  Using CustomValidator VS.  I'm a newbie to this.  Any help greatly appreciated.
Code in aspx.cs   (Code Behind):
protected void ValidateCaptcha(object sender, ServerValidateEventArgs args)
{
                var see = txtimgcode.Text;
                if (Session["CaptchaImageText"]!= null)
                {
    &n ...