Error when creating a new Master page

I created a new Master page for the Checkout pages and I get this error:

<% if (this.SettingManager.GetSettingValueBoolean("Common.EnableWishlist")){ %> . . . 

(a red line appears under 'SettingManger")

'ASP.masterpages_rootckout_master' does not contain a definition for 'SettingManager' and no extension method 'SettingManager' accepting a first argument of type 'ASP.masterpages_rootckout_master' could be found (are you missing a using directive or an assembly reference?)

Header :

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="RootCkOut.master.cs" Inherits="NopSolutions.NopCommerce.Web.MasterPages.RootCkOut" %>

I have this in the code behind :

using NopSolutions.NopCommerce.BusinessLogic.Configuration.Settings;
using NopSolutions.NopCommerce.BusinessLogic.Infrastructure;
using NopSolutions.NopCommerce.BusinessLogic;
using NopSolutions.NopCommerce.BusinessLogic.Content.Forums;
using NopSolutions.NopCommerce.Common.Utils;

I copied the code exactly from root Master page into this new one. Why is it doing this?