PhotoAlbum.cs Resource.Drawable error

[Brown69]

I have copied the code as is on your source code

    static Photo[] mBuiltInPhotos = {
        new Photo ( Resource.Drawable.buckingham_guards,
                    "Buckingham Palace" ),
        new Photo ( Resource.Drawable.la_tour_eiffel,
                    "The Eiffel Tower" ),
        new Photo ( Resource.Drawable.louvre_1,
                    "The Louvre" ),
        new Photo ( Resource.Drawable.before_mobile_phones,
                    "Before mobile phones" ),

But I get errors on those, and the error is " 'Resource.Drawable' does not contain a definition for 'buckingham_guards'