Problems on including Custom Posts on Custom Menus

Hello everybody

I’ve got problem on including a Custom Post into a Custom menu. Here’s the code of the costum post created:

function create_product_post_type() {
	register_post_type( 'products',
		array(
			'labels' => array(
				'name' => __( 'Prodotti' ),
				'singular_name' => __( 'Prodotto' ),
				'add_new' => __('Aggiungi nuovo', 'prodotto', 'your_text_domain'),
				'add_new_item' => __('Aggiungi nuovo prodotto', 'your_text_domain'),
				'edit_item' => __('Edit prodotto', 'your_text_domain'),
				'new_item' => __('Nuovo prodotto', 'your_text_domain'),
				'all_items' => __('Tutti i prodotti', 'your_text_domain'),
				'view_item' => __('Guarda prodotto', 'your_text_domain'),
				'search_items' => __('Cerca prodotti', 'your_text_domain'),
				'not_found' =>  __('Nessun prodotto trovato', 'your_text_domain'),
				'not_found_in_trash' => __('Nessun prodotto in Trash', 'your_text_domain'),
				'parent_item_colon' => '',
				'menu_name' => __('Prodotti', 'your_text_domain')
			),
		'public' => true,
        	'menu_position' => 5,
		'rewrite' => array('slug' => 'prodotti'),
		'can_export' => true,
		'exclude_from_search' => false,
		'has_archive' => false,
		'hierarchical' => true,
		'label' => 'Products',
		'public' => true,
		'publicly_queryable' => true,
		'query_var' => 'products',
		'show_ui' => true,
		'show_in_menu' => true,
		'show_in_nav_menus' => true,
		'supports' => array ( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'comments' ),

		)
	);
}

The Custom Post appear correctly on the Menu page, but when I select it and try to include in a Custom Menu, it shows a it tells me that it is “Not valid” as you can see in the picture below

link img

I also tried with a taxonomy created for the Custom Post, in order to select it and include it in the menu, but nothing changed, same problem.
Any clue?

thanks
Paolo