This way
<asp:CreateUserWizard ID="CreateUserWizard1" runat="server" OnCreatingUser = "CreateUserWizard1_CreatedUser">
<WizardSteps>
<asp:CreateUserWizardStep ID="CreateUserWizardStep1" runat="server">
<ContentTemplate>
<asp:TextBox runat = "server" ID = "Answer" />
<asp:TextBox runat = "server" ID = "Question" />
<asp:TextBox runat = "server" ID = "Email" />
<asp:TextBox runat = "server" ID = "Password" />
<asp:TextBox runat = "server" ID = "UserName" />
<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" />
<asp:Label ID="lblError" runat="server" Text="Invalid captcha" Visible = "false"></asp:Label>
</ContentTemplate>
</asp:CreateUserWizardStep>
</WizardSteps>
</asp:CreateUserWizard>
protected void CreateUserWizard1_CreatedUser(object sender, LoginCancelEventArgs e)
{
MSCaptcha.CaptchaControl Captcha1 = (CreateUserWizardStep1.ContentTemplateContainer.FindControl("Captcha1") as MSCaptcha.CaptchaControl);
TextBox txtCaptcha = (TextBox)CreateUserWizardStep1.ContentTemplateContainer.FindControl("txtCaptcha");
Captcha1.ValidateCaptcha(txtCaptcha.Text);
if (!Captcha1.UserValidated)
{
CreateUserWizardStep1.ContentTemplateContainer.FindControl("lblError").Visible = true;
e.Cancel = true;
return;
}
//Save user to database here
}