  Linear codes for error detection on a q-ary symmetric channel are studied. It
is shown that for given dimension k and minimum distance d, there exists a
value \mu(d,k) such that if C is a code of length n >= \mu(d,k), then neither C
nor its dual are good for error detection. For d >> k or k << d good
approximations for \mu(d,k) are given. A generalization to non-linear codes is
also given.
