I'm going to guess it's a comm issue... those systems are not shielded very well, and when you go shooting tens of kV around a small container, you're bound to get bit errors. Any on-board memory is also quite suspect as these guys use the cheapest possible (even factory rejects). I've also suggested in the past that the control programs have memory leaks, which could cause the creation of faulty vector files or faulty communications if memory is overwritten by other programs who play by the rules. Could be quite a few things, actually.
If you use the same file, does it happen in the same space every time? If not, it's not the file. Can you try a USB cable that converts to a parallel port at the end (can be had for <$10 online)?