Machine was operating fine. Went to load on trailer and my son who was operating engaged the parking brake when he got out of the machine. He disengaged the brake and then couldn't get the brakes to unlock. He has hydraulics just the wheels will jump forwards and backwards but it won't move. the machine wheels will move enough to move the machine to rock back and forth but won't move enough to move the machine. Tried killing machine and letting it sit and restarting and can't get it to unlock the brakes. The light just flashes.