case "SKU":
                    c = LoadAndBindControl("/Store/ProductSummary/SKU.ascx");
                    break;

I need to create SKU.ascx, I copied the file from ProductName.ascx, but there is errors. so I need to change the script.

These are my changes :

Script is sku:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="sku.ascx.cs" Inherits="Controls_ProductSummary_sku" %>
<%# GetSku((string)Product.Sku) %>

 Code in sku.ascx.cs:

public partial class Controls_ProductSummary_sku : ProductSummaryUserControl {
    private const int maxLengthToDisplay = 10;

    protected void Page_Load(object sender, EventArgs e) {

    }
    protected string GetSku(string productSku)
    {
        if (string.IsNullOrEmpty(productSku))
            return string.Empty;

        if (productSku.Length <= maxLengthToDisplay)
            return productSku;

        return productSku.Substring(0, maxLengthToDisplay) + " ...";
    }

}

and the eror message :
Compiler Error Message: CS1061: 'DotShoppingCart.Commercial.Core.Product' does not contain a definition for 'Sku' and no extension method 'Sku' accepting a first argument of type 'DotShoppingCart.Commercial.Core.Product' could be found (are you missing a using directive or an assembly reference?)