Attempting to develop a 1.1 app in C# and when using RegisterScriptableObject I get

Error 2 'System.Windows.WebApplication' does not contain a definition for 'RegisterScriptableObject' and no extension method 'RegisterScriptableObject' accepting a first argument of type 'System.Windows.WebApplication' could be found (are you missing a using directive or an assembly reference?) 

here is the code

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Browser;

namespace TestSilverlight
{
     public partial class Page : Canvas
    {
         public Page()
         {
                  //Register the scriptable endpoints
                  WebApplication.Current.RegisterScriptableObject("basic", this);
         }
        public void Page_Loaded(object o, EventArgs e)
        {
               // Required to initialize variables
               InitializeComponent();
        }
   }

}