Put a single wheel bolt loosely into the hub, get a 10lb mallet and hit the rotor where the caliper used to lie (Very hard). Make sure you've got the park brake off while you're removing the rotor, I've seen that before.
I once hit a rotor off even though I'd forgoten to remove the hex screw, I broke a small piece around the screw and got the rest of the rotor off......I wondered why I had to hit it more and once for a change
