  We determine the mass of the lightest quark-antiquark scalar meson with I=1
using the simulation with two dynamical Domain Wall Fermions. The conventional
exponential fit of the scalar correlator is justified in this case giving the
mass 1.58 +/- 0.34 GeV. In general the scalar correlator receives also the
bubble contribution, which is the intermediate state with two pseudoscalar
mesons. This contribution is sizable at light quark masses and has to be
incorporated in the fit of the scalar correlator in order to extract the scalar
meson mass. We provide predictions for the bubble contribution in Partially
Quenched ChPT, Staggered ChPT and ChPT for Mixed quark actions. We find that
the bubble contribution is significantly affected by the unphysical
approximations that are employed in simulations. It can render the negative
sign and unphysical effective mass 2*Mpi in the scalar correlator with I=1.
