Forms Data Controls :: Compiler Error Message "CS1061: To Do With Gridview Method" When Creating Shopping Cart

I am using an application from a book for a shopping application , to adapt for my own learning, but there seems to be a problem with the shopping cart page. This is a section I have not changed as there is no need to but there is an error. In the code behind the only thing new is the namespace:

namespace OIClothing
{
public partial class Cart : System.Web.UI.Page
{
ShoppingCart cart; // it doesn't like this, giving the debug message the type or namespace 'Shopping Cart" could not be found
protected void Page_Load(object sender, EventArgs e)
{
CheckTimeStamps();
if (Session["cart"] == null)
{
cart = new ShoppingCart();
Session["cart"] = cart;
}
else
{
cart = (ShoppingCart)Session["cart"];
}
GridView1.DataSource = cart.GetItems();
if (!IsPostBack)
GridView1.DataBind();
btnCheckOut.Enabled = (cart.Count > 0);
}
protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
cart.DeleteItem(e.RowIndex);
GridView1.DataBind();
}

but when running the page, this error is given: CS1061: 'ASP.cart_aspx' does not contain a definition for 'GridView1_RowDeleting' and no extension method 'GridView1_RowDeleting' accepting a first argument of type 'ASP.cart_aspx' could be found (are you missing a using directive or an assembly reference?)