C# .NET 2013 can't find Class

I am migrating a website (.NET 2008) to a web application (.NET 2013).  I am having an issue where I have a class in the App_Code folder that used all over the place and now it can't find it.  I believe it is because of the new structure folder structure.

I created the web app in .NET 2013 then copied the website to the directory in the 2013 directory and included the files per instructions I found on the web.

As an example of the current directory structure in Solution Explorer.

MyNewApp(1)
- MyNewApp
  -  App_Code
     - AppClass.cs

using System;
using System.ComponentModel;
using System.Collections.Generic;
using System.Collections;
using System.Diagnostics;
using System.Data;
using System.Data.SqlClient;

namespace PremiumAdmin
{
	public class AppClass : System.ComponentModel.Component
	{
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		protected string sConnectionString;
		protected short iUserID;
		protected string sLastError;

Select allOpen in new window

using System;
using System.Data;
using System.Data.SqlClient;
using System.Web;
using System.Web.UI.WebControls;
using PremiumAdmin;  //Having issues resolving here

public partial class baseFrame : System.Web.UI.MasterPage
{
    protected AppClass appClass = (AppClass)HttpContext.Current.Session["appClass"];  //Having issues resolving here
    public delegate void attachDocumentDelegate(int iDoc);
    public attachDocumentDelegate attachDocument;

    protected void Page_Load(object sender, System.EventArgs e)
    {
        pnlHeaderMenu.Visible = true;
    }

Select allOpen in new window

Error I'm receiving now.
The type or namespace name 'AppClass' could not be found (are you missing a using directive or an assembly reference?)      

ANy ideas how to resolve?