Question Database errors in my Kunena forum

DB function failed with error number 5 Out of memory (Needed 20971492 bytes) SQL=SELECT c.*, c.checked_out as checked_out_contact_category, g.name AS groupname, u.name AS editor, COUNT( DISTINCT s2.checked_out ) AS checked_out_count , z.title AS section_name FROM jos_categories AS c LEFT JOIN jos_users AS u ON u.id = c.checked_out LEFT JOIN jos_groups AS g ON g.id = c.access LEFT JOIN jos_content AS s2 ON s2.catid = c.id AND s2.checked_out > 0 LEFT JOIN jos_sections AS z ON z.id = c.section WHERE c.section NOT LIKE "%com_%" AND c.published != -2 GROUP BY c.id ORDER BY z.title, c.ordering LIMIT 0, 20