MySQL interfacing

I’m sure this is something dumb. Why doesn’t this work:

include '../../../wp-blog-header.php';
global $wpdb;
auth_redirect();
global $currentuser;
get_currentuserinfo();
$cron_key = get_option('cp_cron_auth_key');

if ($_GET['k'] == $cron_key) {
//      $query = "SELECT user_id FROM wp_usermeta WHERE meta_key='gender' AND user_id NOT IN (SELECT uid FROM wp_cubepoints WHERE type='newreg')";
        $query = "SELECT user_id FROM $wpdb->usermeta WHERE meta_key='gender'";
        $array = $wpdb->get_results($query);
        $wpdb->print_error();
        $q = 0;
        foreach ($array as $user => $i) {
                $q++;
        }
        printf(__("Finished.", $q));
} else {
        die (__('No permission to view this file.'));
}

?>

When I browse to https://www.mysite.com/script.php?k=mykey it gives me this error:

WordPress database error: []
SELECT user_id FROM wp_usermeta WHERE meta_key='gender'

Which, is not very descriptive. What am I doing wrong?