Lots of those hydro releases don't function. You could also check for a stuck brake. To roll a short distance, lift one rear wheel off the ramp and the differential action will allow the other tire to roll down. Most of these had a double d type wheel hub- but if yours is keyed, slide the wheel off and take the key out and it will roll where you want it to go.

Look in the rear for something to pull out to release the hydro. Might look like a bolt sticking out near the rear hitch area.