is_user_logged_in() problem on network install

The following code works fine in a single-site install, but when I activate a network on the same site I get the following error:

You do not have sufficient permissions to access this page.

Here is the code:

if(!function_exists(‘is_user_logged_in’)) {
require(ABSPATH . WPINC . ‘/pluggable.php’);
}

if ($opts[‘d404_enable’] == 1 && !is_user_logged_in()) { //if detect 404 mode is enabled

$computer_id = $wpdb->escape($_SERVER[‘REMOTE_ADDR’]);

if ($this->d404_checkLock($computer_id)) { //if locked out
die(__(‘Please come back later’));
}

add_action(‘wp_head’, array(&$this,’d404_check’)); //register action
}

Please note this is in the constructor of my plugin code.