Thin rotors or pads don't affect the ABS system, but if you neglect your brakes, you probably neglect your wheel bearings even more. And when THEY get loose, the sensors start throwing weird signals, which causes the controller to freak out.
The quick fix is to push the sensors all the way back in (as was suggested) and pull the caps off the hubs so you can check/tighten the big wheel bearing nuts. If that doesn't work, then you probably need a new sensor or 2, and they ARE ex$pen$ive new. I have one good used rear one for cheap...