  Problems of stabilizing moduli of the type--IIB string theory on toroidal
orientifolds $\T^6/\Z_2$, in presence of worldvolume fluxes on various
D-branes, are considered. For $Z_2$ actions, introducing either O9 or O3
planes, we rule out the possibility of moduli stabilization in a wide class of
models with $\mathcal{N}=1$ supersymmetry, characterized by the type of fluxes
turned on along D-brane worldvolume. Our results, in particular, imply that
Abelian worldvolume fluxes can not by themselves stabilize closed string
moduli, in a consistent supersymmtric model, for above orientifold
compactifications. We also discuss other $Z_2$ orientifolds of $T^6$ and show
that certain other brane wrappings are also ruled out by similar consistency
requirements. In specific setups we consider examples with D9-branes wrapping
on a complex three-torus with its world-volume fluxes taken to be
semi-homogeneous bundles and D7-branes wrapping holomorphic four-cycles of the
complex three-torus carrying world-volume fluxes.
