add_shortcode problem!

Hello, im trying to add some shortcodes to my wordpress, but it give me an error on any of my scripts, here is one of them:

function permalink_thingy($atts) {
	extract(shortcode_atts(array(
		'id' => 1,
		'text' => ""  // default value if none supplied
    ), $atts));

    if ($text) {
        $url = get_permalink($id);
        return "<a href=".$url." rel='nofollow'>$text</a>";
    } else {
	   return get_permalink($id);
	}

}
add_shortcode('permalink', 'permalink_thingy');

I put this on my functions.php i dont know whats the problem.
The error i get is this one:

Fatal error: Call to undefined function add_shortcode() in /home/xxxxx/public_html/wp-includes/functions.php on line 66