  We compute the PSL(2,N)-module structure of the Riemann-Roch space L(D),
where D is an invariant non-special divisor on the modular curve X(N), with N >
5 prime. This depends on a computation of the ramification module, which we
give explicitly. These results hold for characteristic p if X(N) has good
reduction mod p and p does not divide the order of PSL(2,N). We give as
examples the cases N=7, 11, which were also computed using GAP. Applications to
AG codes associated to this curve are considered, and specific examples are
computed using GAP and MAGMA.
