Database error in vBulletin 3.7.6:

Invalid SQL:
SELECT *,
IF(displaygroupid=0, usergroupid, displaygroupid) AS displaygroupid
 FROM user WHERE usergroupid = '2' ORDER BY RAND() LIMIT 30;

MySQL Error   : Incorrect key file for table '/tmp/#sql_339_0.MYI'; try to repair it
Error Number  : 126