locking error

[Kenneth Vogt]

Why does the following get the error: Table 'am_queue' was not locked with LOCK TABLES

LOCK TABLES am_queue READ, am_group READ, am_site READ;
(
SELECT am_group.description AS partner, am_queue.action_date AS action_date
FROM am_queue
LEFT JOIN am_group ON am_queue.site_id = am_group.id
WHERE am_queue.status = 'complete'
AND am_queue.action_type = 'post'
GROUP BY partner
)
UNION (

SELECT am_site.description AS partner, am_queue.action_date AS action_date
FROM am_queue
LEFT JOIN am_site ON am_queue.site_id = am_site.id
WHERE am_queue.status = 'complete'
AND am_queue.action_type = 'submit'
GROUP BY partner
)
ORDER BY action_date DESC
LIMIT 10;
UNLOCK TABLES;