Error: Table drupal.nodeaccess_role_alias doesn't exist

Watchdog (/admin/logs/watchdog) reports the following error:

Table 'drupal.nodeaccess_role_alias' doesn't exist query: SELECT r.rid, r.name, a.name AS alias, a.weight FROM role r LEFT JOIN nodeaccess_role_alias a ON r.rid = a.rid ORDER BY r.name in /var/www/drupal/includes/database.mysql.inc in Zeile 174.

What does this mean? Why has this table not been created if it is needed? Why does Watchdog log an error is the table is optional?

Regards, -asb