Thank you for your reply. I have checked the case of the names and they all match, I did noticed the OrderDB's name space was Portal.App_Code and the codebehind for the page I want to use it on was using namespace Purchasing.  So I changed OrderDB to use the namespace Purchasing however this has not helped.  I have posted my code for both items and the directories they are in so perhaps you can pinpoint much better than I can what is wrong.

/Purchasing/Checkout.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web.Security;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

namespace Portal.Purchasing
{
    public partial class Checkout : System.Web.UI.Page
    {
        private Order order;
        private Customer cust;
        private ShoppingCart cart;
        protected void Page_Load(object sender, EventArgs e)
        {
            cart = (ShoppingCart)Session["cart"];

            if (Session["order"] == null)
            {
                order = new Order(DateTime.Now,
                    null, (ShoppingCart)Session["cart"]);
                Session["order"] = order;
            }
            else
            {
                order = (Order)Session["order"];
                cart = order.Cart;
            }

            cust = new Customer(txtLastName.Text, txtFirstName.Text, txtEmail.Text);
            order.Cust = cust;

            lblSubtotal.Text = order.SubTotal.ToString("c");
            lblShipping.Text = order.Shipping.ToString("c");
            lblTotal.Text = order.Total.ToString("c"); cart = (ShoppingCart)Session["cart"];

            if (Session["order"] == null)
            {
                order = new Order(DateTime.Now,
                    null, (ShoppingCart)Session["cart"]);
                Session["order"] = order;
            }
            else
            {
                order = (Order)Session["order"];
                cart = order.Cart;
            }

            cust = new Customer(txtLastName.Text, txtFirstName.Text, txtEmail.Text);
            order.Cust = cust;

            lblSubtotal.Text = order.SubTotal.ToString("c");
            lblShipping.Text = order.Shipping.ToString("c");
            lblTotal.Text = order.Total.ToString("c");
        }
        protected void Wizard1_FinishButtonClick(object sender, WizardNavigationEventArgs e)
        {

            bool success = Portal.Purchasing.OrderDB.WriteOrder(order);
            Session["cart"] = null;
            Session["order"] = null;
            if (success)
                Response.Redirect("Completed.aspx");
            else
                Response.Redirect("Completed.aspx?Error=1");
        }
    }
}

/App_Code/OrderDB.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.SqlClient;

namespace Portal.Purchasing
{
    public class OrderDB
    {
        static SqTransaction tran;
        static SqlConnection con;
        public static bool WriteOrder(Order o)
        {
            string cs = WebConfigurationManager
                .ConnectionStrings["MuirHubProductsConnection"]
                .ConnectionString;
            con = new SqlConnection(cs);
            con.Open();
            tran = con.BeginTransaction();
            try
            {
                InsertCustomer(o.Cust);
                int oNum = InsertOrder(o);
                foreach (CartItem item in o.Cart.GetItems())
                    InsertItem(item, oNum);
                tran.Commit();
                con.Close();
                return true;
            }
            catch (Exception ex)
            {
                tran.RollBack();
                return false;
            }
        }

        private static void InsertCustomer(Customer cust)
        {
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.Transaction = tran;
            try
            {
                cmd.CommandText = "INSERT INTO Staff "
                    + "(lastname, firstname, email) "
                    + "VALUES (@LastName, @FirstName, @Email)";
                cmd.Parameters.AddWithValue(
                    "@LastName", cust.LastName);
                cmd.Parameters.AddWithValue(
                    "@FirstName", cust.FirstName);
                cmd.Parameters.AddWithValue(
                    "@Email", cust.Email);
                cmd.ExecuteNonQuery();
            }
            catch (SqlException ex)
            {
                if (ex.Number == 2627) //DuplicateKey
                {
                    cmd.CommandText = "UPDATE Staff "
                        + "SET lastname = @LastName, "
                        + "firstname = @FirstName "
                        + "WHERE email = @Email ";
                    cmd.ExecuteNonQuery();
                }
                else
                    throw ex;
            }

        }
        private static int InsertOrder(Order o)
        {
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.Transaction = tran;
            cmd.CommandText = "INSERT INTO Orders "
                + "(orderdate, custemail, "
                + "subtotal, shipping) "
                + "VALUE (@OrderDate, @Custemail, "
                + "@subtotal, @shipping)";
            cmd.Parameters.AddWithValue(
                "@OrderDate", DateTime.Now);
            cmd.Parameters.AddWithValue(
                "@Custemail", o.Cust.Email);
            cmd.Parameters.AddWithValue(
                "@subtotal", o.SubTotal);
            cmd.Parameters.AddWithValue(
                "@shipping", o.Shipping);
            cmd.ExecuteNonQuery();
            cmd.CommandText = "SELECT @@IDENTITY";
            return Convert.ToInt32(cmd.ExecuteScalar());
        }
        private static void InsertItem(CartItem item,
            int oNum)
        {
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.Transaction = tran;
            cmd.CommandText = "INSERT INTO OrderItems "
                + "(ordernum, productid, "
                + "name, price, quantity_ "
                + "VALUES (@OrderNum,, @ProductID, "
                + "@Name, @Price, @Quantity)";
            cmd.Parameters.AddWithValue(
                "@OrderNum", oNum);
            cmd.Parameters.AddWithValue(
                "@ProductID", item.ID);
            cmd.Parameters.AddWithValue(
                "@Name", item.Name);
            cmd.Parameters.AddWithValue(
                "@Price", item.Price);
            cmd.Parameters.AddWithValue(
                "@Quantity", item.Quantity);
            cmd.ExecuteNonQuery();
        }
    }
}