There are two possibilities: your photoresist is poorly adhered to the wafer or
your PDMS is too sticky because of the mixing ratio. You should try to hard bake
your wafer @ 150 for 30 minutes b4 putting on PDMS. if that doesn't solve the
problem, try the other kind of PDMS (I assume that you are awared of the two
popular types of PDMS, one is less sticky than the other)

  good luck.

  H.