custom post type with category permalink (page not found)

I create a custom post type and it work find until I decided to change the permalink if my permalink look like this /blog/post-name it work find but if i change it to this /blog/category/post-name the page is not found.

this is my code:

// Add custom post page
add_action( 'init', 'create_post_type' );
function create_post_type() {
register_post_type('blog', array(
'label' => 'Blog',
'public' => true,
'show_ui' => true,
'show_in_nav_menus' => false,
'capability_type' => 'post',
'hierarchical' => true,
'rewrite' => array('slug' => 'blog/%cat%'),
'menu_position' => 5,
'with_front' => true,
'taxonomies' => array('blog-cat'),
'query_var' => true,
'publicly_queryable' => true,
'supports' => array('title', 'editor', 'thumbnail',
)
) );
}

//Add new taxonomy upon WordPress initialization
add_action( 'init', 'blog_create_taxonomies', 0 );

function blog_create_taxonomies()
{
    // Project Categories
    register_taxonomy('blog-cat',array('blog'),array(
        'hierarchical' => true,
        'label' => 'Blog Categories',
        'singular_name' => 'Blog Category',
        'show_ui' => true,
        'query_var' => 'blog-cat',
        'show_admin_column'     => true,
        'rewrite' => array('slug' => 'blog-cat', 'with_front' => true)
    ));
}

/*Filtro per modificare il permalink*/
add_filter('post_link', 'cat_permalink', 1, 3);
add_filter('post_type_link', 'cat_permalink', 1, 3);

function cat_permalink($permalink, $post_id, $leavename) {
	//con %brand% catturo il rewrite del Custom Post Type
    if (strpos($permalink, '%cat%') === FALSE) return $permalink;
        // Get post
        $post = get_post($post_id);
        if (!$post) return $permalink;

        // Get taxonomy terms
        $terms = wp_get_object_terms($post->ID, 'blog-cat');
        if (!is_wp_error($terms) && !empty($terms) && is_object($terms[0]))
        	$taxonomy_slug = $terms[0]->slug;
        else $taxonomy_slug = 'no-cat';

    return str_replace('%cat%', $taxonomy_slug, $permalink);
}