Databinding PasswordBox through Attached properties

Hi,
I've read in a few places that there's no Dependency Properties attached to the Password Box in WPF and the work around is through Attached Properties. I've found a couple of blogs which show how to do this. This is what I have in my code:

namespace WPFApplication2
{
    public class BoundPasswordBox
    {
        #region BoundPassword
        private static bool _updating = false;

        /// <summary>
        /// BoundPassword Attached Dependency Property
        /// </summary>
        public static readonly DependencyProperty BoundPasswordProperty =
            DependencyProperty.RegisterAttached("BoundPassword",
                typeof(string),
                typeof(BoundPasswordBox),
                new FrameworkPropertyMetadata(string.Empty, OnBoundPasswordChanged));

        /// <summary>
        /// Gets the BoundPassword property.
        /// </summary>
        public static string GetBoundPassword(DependencyObject d)
        {
            return (string)d.GetValue(BoundPasswordProperty);
        }

        /// <summary>
        /// Sets the BoundPassword property.
        /// </summary>
        public static void SetBoundPassword(DependencyObject d, string value)
        {
            d.SetValue(BoundPasswordProperty, value);
        }

        /// <summary>
        /// Handles changes to the BoundPassword property.
        /// </summary>
        private static void OnBoundPasswordChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e)
        {
            PasswordBox password = d as PasswordBox;
            if (password != null)
            {
                // Disconnect the handler while we're updating.
                password.PasswordChanged -= PasswordChanged;
            }

            if (e.NewValue != null)
            {
                if (!_updating)
                {
                    password.Password = e.NewValue.ToString();
                }
            }
            else
            {
                password.Password = string.Empty;
            }
            // Now, reconnect the handler.
            password.PasswordChanged += new RoutedEventHandler(PasswordChanged);
        }

        /// <summary>
        /// Handles the password change event.
        /// </summary>
        static void PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox password = sender as PasswordBox;
            _updating = true;
            SetBoundPassword(password, password.Password);
            _updating = false;
        }

        #endregion
    }
}

And this is my Corresponding XAML Code:

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        xmlns:ff="clr-namespace:WpfApplication2;assembly=WpfApplication2"><Grid><PasswordBox HorizontalAlignment="Left" Height="32" Margin="60,110,0,0" VerticalAlignment="Top" Width="122"
                     ff:BoundPasswordBox.BoundPassword="{Binding Path=Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/></Grid></Window>

But, when I build the solution, it throws an error:
The property 'BoundPasswordBox.BoundPassword' does not exist in XML namespace
The attachable property 'BoundPassword' was not found in type 'BoundPasswordBox'.  

Any help would be appreciated

---

Abhi