Make sure you turn the regen off button while the tractor is on, then turn the tractor off. The regen off should stay illuminated for several seconds when the ignition is off. When the light goes out, press the regen button to off and start the tractor. Then follow the steps. Very frustrating...
I've had issues with my RK37 doing the exact same thing to the extent I had to have a forced regen with the diagnostic tool. However, I have found if I follow these steps I can get it to go into regen.
1. Engine running at idle speed
2. Push the block regen button to the left of the regen...