PDO Exception: SQLSTATE[HY000]: General error: 2008 MySQL client ran out of memory

I'm currently purging a phpbbforum into Drupal and when running PhpbbPost from the migrate module, this error is displayed:

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /batch?render=overlay&id=15661&op=do StatusText: Service unavailable (with message) ResponseText: PDOException: SQLSTATE[HY000]: General error: 2008 MySQL client ran out of memory: SELECT t.topic_first_post_id AS topic_first_post_id, p.post_id AS post_id, p.poster_id AS poster_id, p.poster_ip AS poster_ip, p.post_time AS post_time, p.post_edit_time AS post_edit_time, p.post_approved AS post_approved, p.post_subject AS post_subject, p.post_text AS post_text, p.bbcode_uid AS bbcode_uid, map.destid1 AS migrate_map_destid1, map.needs_update AS migrate_map_needs_update FROM {posts} p LEFT OUTER JOIN {topics} t ON p.topic_id = t.topic_id LEFT OUTER JOIN {SITENAME_phpb_dev.migrate_map_phpbbpost} map ON post_id = map.sourceid1 WHERE (post_approved = :db_condition_placeholder_0) AND (p.post_id <> t.topic_first_post_id) AND( (map.sourceid1 IS NULL ) OR (map.needs_update = :db_condition_placeholder_1) ) ORDER BY post_time ASC; Array ( [:db_condition_placeholder_0] => 1 [:db_condition_placeholder_1] => 1 ) in MigrateSourceSQL->performRewind() (line 318 of /home/SITENAME/dev/sites/all/modules/migrate/plugins/sources/sql.inc).

Help, please.