MySQL 5.1 lost its connection during query

I'm using Solaris as my operating system and everytime I execute my query in mysql server, it replies to me error. It says, "Lost connection to MySQL server during query". I'm using I am using mysql 5.1. What can I do to get rid of this issue?
MY QUERY IS:
ELECT post_time, p.topic_id, t.topic_replies, post_id, u.user_id, username
FROM jforum_posts p, jforum_users u, jforum_topics t , jforum_forums f
WHERE t.forum_id = f.forum_id
AND t.topic_id = p.topic_id
AND f.forum_last_post_id = t.topic_last_post_id
AND t.topic_last_post_id = p.post_id
AND p.forum_id = 1
AND p.user_id = u.user_id
AND p.need_moderate = 0;
