SQL-DATABASE ERROR

Database error in WoltLab Burning Board (2.1.5): Invalid SQL: SELECT m.*, m.userid AS moderatorid,b.* FROM bb2_boards b LEFT JOIN bb2_moderators m ON (m.boardid=b.boardid AND m.userid='0') WHERE b.boardid = '28'
mysql error: Out of resources when opening file './usr_web1_15/bb2_moderators.MYD' (Errcode: 24)
mysql error number: 23
mysql version: 5.5.47-0+deb6u1-log
php version: 5.3.3-7+squeeze29
Date: 04.07.2020 @ 08:50
Script: /board.php?boardid=28
Referer: