I think that it is unlikely that the button is the problem as I said in my original post the printer makes an audible tone when the button is pushed, which indicates that the controller card is acknowledging the button press and as I also said turning the power on an off does not clear the problem.
The printer was left to print a job over the weekend which it completed sucessfully. When we checked the printer on Monday morning we saw the problem. Since posting the original message I have spoken to our firmware engineers and they think that it is probably a firmware bug, possibly a buffer over run, which has happen because the printer was left for a long period without the button being pushed to acknowledge the message on the screen.
We are sill waiting for our reseller to get back to us, but if we have not heard from him shortly we are going to access the controller card directly and see if we can resolve the issue, as a first step we are going to plug a monitor into the HDMI port and see what happens when the printer boots up.