DB QUERY ERROR (one_row_query()): Can't open file: './thab_2016/admin_modules_seo.frm' (errno: 24 - Too many open files)

SELECT IF(CHAR_LENGTH(seo_title), seo_title, (SELECT name FROM admin_modules WHERE moduleid = 2)) AS seo_title, seo_keywords, seo_description FROM admin_modules_seo WHERE groupid = 2 AND moduleid = 2