Craftsman 46" mower won't stay running?

I have a 1997 Craftsman 20.5 Hp Kohler engine, 46" cut , hydrostatic drive garden tractor, model 944.607201. My problem is that the tractor will start just fine with the brake/clutch pushed in, but as soon as I attempt to disengage the clutch, engage the blade drive, or shift it out of the Neutral position the engine quits. I checked the operation of the safety switch on the seat thinking that it was faulty, but it appears fine. I tried bypassing this sitch to be sure and the engine still konks out as soon as I attempt to either move it, engage the blades, or release the clutch. Any thoughts??