  We propose an alternative explanation to the oscillations of the flux-flow
resistance found in several previously published experiments with BiSrCaCuO
stacks. It has been argued by the previous authors that the period of the
oscillations corresponding to the field needed to add one vortex per two
intrinsic Josephson junctions is associated with a moving triangular lattice of
vortices (out-of-phase mode), while the period corresponding to one vortex per
one junction is due to the square lattice (in-phase mode). In contrast, we show
that both type of oscillations may occur in a single-layer Josephson junction
and thus the above interpretation is inconsistent.
