  We show the (already known) fact that Randall-Sundrum scenarious although
compatible with a ${\mathbb{Z}}_2$ orbifold symmetry cannot hold regularity of
the fields at the orbifold planes in the absence of boundary actions and
respective jumps of the fields. This makes the models mathematical
inconsistence and invalidate the inclusion of such models in a higher
dimensional theory such as string theory. For completeness we point out some
directions already in the literature and in progress.
