MyBB SQL Error

MyBB has experienced an internal SQL error and cannot continue.

SQL Error:
2006 - MySQL server has gone away
Query:
SELECT `mybb_threads`.fid, `mybb_threads`.tid, `mybb_threads`.tag, `mybb_threads`.subject, `mybb_forumpermissions`.canview FROM `mybb_threads` LEFT JOIN `mybb_forumpermissions` ON `mybb_forumpermissions`.canview = 0 WHERE MATCH (`mybb_threads`.subject) AGAINST ('مددکاری اجتماعی و پیشگیری از جرم' IN BOOLEAN MODE) LIMIT 8