Which VFD do you have? When I first got my mill I had the C300 vfd. I had issues with the smooth stepper. I don't remember the exact message but something like out of data. I also had trouble with the power draw bar. The display would show random gibberish characters and lock up. Novakon determined that the problem was probably electrical noise from the VFD. They sent me a GS2 VFD. The two issues I mentioned went away and did not return. If you already have a GS2 maybe check the connections? Make sure the wiring is tight as it can be a source of errors.
I have since switched to an Acorn control and I'm currently testing it.