Put some pressure on it with a pry bar. We just did mine yesterday and ran into the same problem. It needs to have some load on it to hold it in place while you remove the nut. Then you'll need to do the same thing when tightening it back up. Kind of a pain in the
but you'll get it. If you get too frustrate stop for a minute, catch your breath, and crack open a cold one (juice that is).