[Plugin: WP-reCAPTCHA] Error Call to undefined function wp_get_current_user()

Hello, has faced such problem. At installation on WordPressMU under the instruction on a site (version WordPress 3.0.1)? All site falls in an error:
Fatal error: Call to undefined function wp_get_current_user () in /var/www/hobit/data/www/hob-bit.ru/wp-includes/user.php on line 223

In lines 222-225 there is a following:

function get_current_user_id () {
$user = wp_get_current_user ();
return (isset ($user-> ID)? (int) $user-> ID: 0);
}

Prompt a solution of a problem.

P.S. Forgive for broken English, I from Russia.