Find Captcha and TextBox control inside ASP.Net CreateUserWizardStep

I am integrating a Captcha control inside a CreateUserWizard.
 
As I wanted to do a validation for user's input based on the Captcha using an if.. else.. statement. However an error occured when I trying to get the Captcha control from the createuserwizard.
 
Here the is error : 

The name 'Captcha1' does not exist in the current context 

I had tried to get this control as a textbox, image, control but it was not successful.
 
Here is the code :

 <asp:CreateUserWizardStep ID="CreateUserWizardStep1" runat="server">
              <ContentTemplate>

 <tr>
                            <td class="style4">Answer:</td>
                            <td>
                                <cc1:CaptchaControl ID="Captcha1" runat="server"
                                 CaptchaBackgroundNoise="Medium" CaptchaLength="5"
                                 CaptchaHeight="55" CaptchaWidth="200"
                                 CaptchaLineNoise="None" CaptchaMinTimeout="5"
                                 CaptchaMaxTimeout="240" FontColor = "#FF33CC" CaptchaFontWarping="Medium" />

                                 <asp:TextBox runat="server" ID="txtCaptcha" />

                            </td>
                        </tr>
 </ContentTemplate>

              </asp:CreateUserWizardStep>

Code behind: 

protected void CreateUserWizard1_CreatedUser(object sender, EventArgs e)
    {
        //Control Captcha1 = (Control)CreateUserWizardStep1.ContentTemplateContainer.FindControl("Captcha1");
        TextBox txtCaptcha = (TextBox)CreateUserWizardStep1.ContentTemplateContainer.FindControl("txtCaptcha");

            Captcha1.ValidateCaptcha(txtCaptcha.Text.Trim());//error occurred here

        if (Captcha1.UserValidated)//error occurred here
        {

     }

}