Husqvarna MZ6128ZT, One blade Not turning

It is about 18 months old with about 70 hrs on it. I'm out of town at the moment and my BIL was mowing for me and sucked a plastic tarp under the left side. The engine bogged down and stopped. He cut the tarp off and it started back up fine, but when he engaged the blades, the middle and right blade turned OK but the left blade does not turn. He can turn the blade freely with his hand and it is a little stiff as normal. Looking at the IPB I don't see a shear pin anywhere so it's not obvious what to look for next. Any suggestions are appreciated.



Parts and Diagrams for Husqvarna MZ 6128 (966502301) (2009-10)



Thanx,

Jerry