The SELECT would examine more than MAX_JOIN_SIZE rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is okay

        SELECT p.id_product, pl.id_lang, pl.name as pname, p.reference, p.ean13, pl.description_short, pl.description, cl.name as cname, m.name as mname
        FROM ps_product p
        LEFT JOIN ps_product_lang pl ON p.id_product = pl.id_product
        LEFT JOIN ps_category_lang cl ON (cl.id_category = p.id_category_default AND pl.id_lang = cl.id_lang)
        LEFT JOIN ps_manufacturer m ON m.id_manufacturer = p.id_manufacturer
        WHERE p.indexed = 0

mysql_query('SET GLOBAL SQL_MODE=\'\'', $this->_link);

mysql_query('SET SQL_BIG_SELECTS=1', $this->_link);