Although the other answer to this query may be valid, my (very recent) experience is that it is more likely to be the switch itself that is faulty. I have just had the cover off the dishwasher and 'fooled' the system by shorting across the contacts of the microswitch driven by the button and all works fine.
It is less likely to be the door switch, as the door has to be in the open position anyway for the button to be accessed.
I do not yet know whether I have to buy a whole new circuit board or whether I can solder off the switch and replace, which would obviously be a lot less expensive and seems very possible.
Simon Brock
August 2007