It won't do any good to spray the lugs with penetrating oil, because they're pressed into the hub and come off with the hub. I agree with Shadetree, you will probably need a hub puller to get that off, since you can't turn the adjusters to back off the brake shoes.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.