Originally Posted by PerryB

It looks to me like that washer has its tab broken off and is in a bind on the spindle threads. Rotate it clockwise to align the tab with the slot in the spindle and I think it'll come right off. Also while you're that far into it, pull the spindles and service the axle support bearings inside the spindle. You'd be amazed how many people don't know about that bearing being in there.