I have had issues in the past that did the same thing. In my case it was how I wrote or edited a program. In my case, I was hitting the O key instead of the 0. The two keys are right next to each other and if I have the wrong glasses or am in a hurry it used to happen. I finally put a piece of tape over the O key so that i wasn't distracted into hitting the wrong key. This is probably not what is happening in your case but worth checking if you are manually writing your program. You said it did this on the first G00. What about any other G00's?