  The propagation of damage in a confined magnetic Ising film, with short range
competing magnetic fields ($h$) acting at opposite walls, is studied by means
of Monte Carlo simulations. Due to the presence of the fields, the film
undergoes a wetting transition at a well defined critical temperature $T_w(h)$.
In fact, the competing fields causes the occurrence of an interface between
magnetic domains of different orientation. For $T < T_w(h)$ ($T > T_w(h)$) such
interface is bounded (unbounded) to the walls, while right at $T_w(h)$ the
interface is essentially located at the center of the film.
  It is found that the spatio-temporal spreading of the damage becomes
considerably enhanced by the presence of the interface, which act as a
''catalyst'' of the damage causing an enhancement of the total damaged area.
The critical points for damage spreading are evaluated by extrapolation to the
thermodynamic limit using a finite-size scaling approach. Furthermore, the
wetting transition effectively shifts the location of the damage spreading
critical points, as compared with the well known critical temperature of the
order-disorder transition characteristic of the Ising model. Such a critical
points are found to be placed within the non-wet phase.
