My 2001 Duke ll did something similar. The nut came off (they are supposedly
loc-tit'd at the KTM factory!) but in my case the little plastic countershaft
cover held the sprocket and nut on even though they were spinning free, the sprocket moved over enough to spin so I had no drive. But nothing got tangled up. Slipped back on and tightened it best I could by the side of the
road. It was loose again by the time I did 30 miles and home.
My dealer says this is, unfortuneatley, fairly common. He reccomended a
new nut and washer and RED Loctite. I did this, never had it happen again.
Here on the forums and elesewhere I've also read many reports of this same
Glad you didn't bust open the engine case!