Catalyzes oxidation of D-erythronate to 2-oxo-tetronate. Can use either NAD(+) or NADP(+) as cosubstrate, with a preference for NAD(+). D-erythronate + NAD(+) = 2-dehydro-D-erythronate + H(+) + NADH kcat is 1.9 sec(-1) with NAD(+) as cosubstrate. kcat is 0.88 sec(-1) with NADP(+) as cosubstrate. Belongs to the NAD(P)-dependent epimerase/dehydratase family.