Hello, first thing I would check on all of your machines is the serial numbers, what you are looking for is to see if there is a 35 within the serial. Should you find one, I would suggest letting HP know because it is within that range that these machines were defective from the manufacturer, and will get the error you have experienced.
As to fixing the issue, you will need to replace the printbar, as well as, a special tool that you will need to keep the printbar from falling. Another thing, you will have to take this machine almost completely apart to replace the printbar. It is not too bad, as I have done it once already, but you will need a manual, the special tool, and printbar. Further bad news, is I am unsure if HP has made the part number for the printbar available yet. As the numbers in the service manual are incorrect.
Basically, there is an issue with the printbar, after so many prints I believe 2,000 or a little over that you will get this error code, if it falls into the serial number range with 35.
Hope this helps....And good luck if you decide to repair them yourself.