If your controllers are identical models, and one is acting up, I would suspect some kind of hardware malfunction, such as a failing circuit board. I have no idea what your controller looks like inside, though, so you'd best get a real service technician on the phone for help.
If the controller tells you that there is an error, is this just "after the fact" when it does an in-position check when the arc is completed, and then attempts to correct it, or does it halt with an error before it does the faulty arc?