Are you engaging the blades at full throttle, half throttle, or idle? Does that unit use an electric clutch or a manual one? electric clutches use a pull up knob, while manual ones use a lever. Is your deck clean of caked on grass, etc?
Could be a safety switch, my mothers craftsman the engine will stop running if you engage the mower and you are not sitting on the seat. I check the switches on your seat.