Yes, it's a genuine, licensed copy. As it turns out, it's not the z-offset that's changing, it's the machine coordinates. As an example, the top of the piece in one of my projects is -2.3. All of the suddent, the machine coordinate changes to +1.5, which moves the perceived zero and ruins the wood. I would think this has to be a mechanical error, such as a motor binding, but I'm not sure. I've changed the z-axis acceleration from 4.0 all the way down to 0.8, with the same problem. I've also had this happen while in the middle of a long, straight cut with no programmed z-axis movement at all--all of the sudden my bit drops about a quarter inch further into the wood. Any ideas?