Which controller do you have on the machine? Is it the old, original controller? The old one is 2 big cases, each somewhere between 1.5 and 2 foot per side? IF you do, your problem may be in there. I also run an old validator, but 3 years ago we upgraded all the controllers on the machine to the Sharpe32 controller. I seem to remember from 7 or 8 years ago that we had to replace one of the control boards for this very reason. Also, something else you need to watch out for, is manually un-seating the head, either by crashing it (doesn't matter how hard) or by over-tightening the TP2 in the head. We have a guy locally who can do a lot of repairs to our PH9. And he has told me that it is basically a thin, flat plate inside the head that holds the head in the locked position. This plate can get bent very easily. In the past (when we had a 'clumsy' programmer) he had to do this a lot to our head. He will flatten this plate out and the head works fine again. If your head changes angle and seats, then un-seats, then seats, then un-seats and gives you the error, I would bet dollars to doughnuts that this is the problem. If it only seats, then un-seats and gives the error, it may be in the controller, but it may still be in the head. I would not recommend that you try to make this repair yourself. I sure wouldn't want to try it!