DB Error: selectList query failed

SELECT SQL_CALC_FOUND_ROWS DISTINCT jedu2_referrals.* FROM jedu2_referrals LEFT JOIN jedu2_referral_category_relations ON jedu2_referral_category_relations.referral_id = jedu2_referrals.id WHERE (category_id = '1')ORDER BY RAND()

Got error 28 from storage engine