We construct several examples where duality transformation commutes with the
orbifolding procedure even when the orbifolding group does not act freely, and
there are massless states from the twisted sector at a generic point in the
moduli space. Often the matching of spectrum in the dual theories is a result
of non-trivial identities satisfied by the coefficients of one loop tadpoles in
the heterotic, type II and type I string theories.Comment: LaTeX file, 19 pages, a new example and references adde
