Pressure in lines on baler can cause that problem, along with others mentioned. In some cases I have
loosened the fittings on the baler hose and let the pressure, and some fluid, leak out, then retighten and try hooking up again. Sometimes just hitting the round ball at the end of the hose connector on the baler hitch will let enough pressure off to work. To keep from happening again, when parking baler, turn tractor off, work the hydraulic levers back and forth to relive pressure.