Add A Custom Base Class For Web Forms?

I want to add a custom base class for all of my web forms. I created a "App_code" folder in my asp.net web project and add a simple base page class like this:

namespace MySite.Web
{
// base page for all the pages that need localization
public class LocalizationPage : System.Web.UI.Page
{
protected override void InitializeCulture()
{
base.InitializeCulture();
}
}
}

And then I try to let asp.net web form to inherit from this base page. I have something like this:

using MySite.Web;

namespace MySite.Public
{
public partial class RegisterPage : LocalizationPage
{
}
}

Now I run into problem where Visual Studio doesn't recognize the LocalizationPage class I created. On the above code snippet, LocalizationPage is not highlighted as a class. And when I try to compile, I got the following error message:

Error 1 The type or namespace name 'LocalizationPage' could not be found (are you missing a using directive or an assembly reference?)