Okay, here's something that may help--I just noticed that the green light on the E-Stop box that indicates that the machine is "enabled" turns off when I push "Move" in the Step Response screen. I'm not sure what the light actually means, but when I start up the machine I have to push a button on the E-Stop box that causes the light to go on. The machine won't do anything unless it's on. Pushing the E-stop button also turns the light off, disabling all axes. Not sure why the Step Response screen would do the same...