Electric clutch will not disengage?

Sears 24 HP Lawn tractor, Model 917.273622. I can hear and see the electro magnetic clutch engage and disengage when I operate the PTO selector switch to engage the blades. The blades stay engaged all the time now, yet I can see the clutch energize and move and de energize as I operate the PTO switch. I was just driving the tractor and the blades all of a sudden started and now they are always turning no matter the position of the switch