Lock the car with a normal remote. Then unlock. Valet should reset. Valet mode is designed so that when your man is left with just the green key he can't open anything.
Mercedes have a separate chauffeur key that only actuates the main doors and ignition. It looks the same as the spare so if you mix them up you suddenly find you can get into the boot/glove box.
Phew, glove box opened. I had the key in one hand and a crow bar in the other!!! Thanks guys, great help. PS: Phone calls where from muy accountant, damn him, reminding me to pay my tax!!