Standard question #2:
What error message do you get?

??? Who on earth advised you to do that...???

Well, since you've now moved your app's functionality (i.e. its classes)
into a separate project, you'll need to add a reference to it... Have you
done that...?

It looks like the code you have moved to another project is directly related
to your website output. Unless you need to use the code in more than one web
project, it would be better to keep this kind of code in the App_Code
folder.

If the code will be used in more than one web project (database code, for
example), it should absolutely be moved to its own class library.

Regardless of where the code lies, I think what you want to do is override
the default Page class. Something like this (forgive the C#, my VB is a bit
rusty):

public class MyPage : System.Web.UI.Page
{
   public Label lblPageHeading;
   // ...

   protected override void OnLoad(EventArgs e)
   {
       // ...
   }
}

Then in your code-behind files, inherit from MyPage instead of
System.Web.UI.Page. For example:

public partial class _Default : MyPage
{
   // ...
}

All of your pages will then inherit the properties and methods from MyPage.