garciasanchezdani on "wp enqueue scripts don't work"

Hi all, I'm using it in a single post, like this:

add_action( 'wp_enqueue_scripts', 'wp_add_unit_scripts' );
function wp_add_unit_scripts() {

    global $post;

    wp_register_script('unit_more_widgets_scripts', WP_PLUGIN_DIR.'/js/funcionalidad.js', array( 'jquery' ));

    if($post->post_author == ID_USUARIO){
        wp_enqueue_script('unit_more_widgets_scripts');
    }
}

I'm calling it just after get_header ... but I'm debugging and the code inside the function isn't executed...

What I try is to add some javascript in one single post, only if this post has been created by determined user...

Thanks, Daniel