I have a Massey Ferguson 4225 with dual remotes out back. When I tried to use them the other day, I had the same problem, no matter how hard I pushed, they would not lock in. To check for backpressure, I turned off the tractor, then worked the remote levers to release any internal pressure. My remotes are manual, but if your's are electric, you should still be able to activate them with the tractor engine off and key on. My problem turned out to be that the Pioneer connectors were stuck because they had not been used in a long time. Used some PB Blaster (same as liquid wrench) and an air hose to blow out the excess and contamination and they hooked right up /forums/images/graemlins/grin.gif
Also check to see if the problem is with the hoses you are connecting having back pressure due to the way your attachment is sitting now or if it was parked in a way that is pressurizing the hoses.
Either way, please be careful!! pressurized hydraulic fluid can be injected into the skin and according to my Bush Hog manual may cause Gangreen if not removed by a doctor within a few hours./forums/images/graemlins/frown.gif
Another caution which I'm sure you realize, is that if the pressure in the hoses is supporting your attachment, it's going to move or possibly fall when you release the pressure!!
Block or chain that thing securely before you loosen any hose fittings. /forums/images/graemlins/tongue.gif
Be safe!