MyBB SQL Error

MyBB has experienced an internal SQL error and cannot continue.

SQL Error:
144 - Table './lg/mybb_posts' is marked as crashed and last (automatic?) repair failed
Query:
SELECT p.pid, p.message, p.tid, p.smilieoff, t.attachmentcount FROM mybb_posts p LEFT JOIN mybb_threads t ON (t.tid=p.tid) WHERE t.visible='1' AND t.fid NOT IN (4) AND t.closed NOT LIKE 'moved|%' AND t.firstpost=p.pid ORDER BY t.dateline DESC LIMIT 0, 10