is_user_logged_in gives me errors

just curios if this function was removed from buddypress? getting this in my log files:

[Tue Oct 19 14:24:03 2010] [warn] mod_fcgid: stderr: PHP Fatal error: Call to undefined function is_user_logged_in() in /var/www/clients/clientxx/webxx/web/unkie/wp-content/plugins/wordpress-mu-secure-invites/secure_invite.php on line 190