Thank you very much RjCorazza. The images came up fine for me, but I appreciate the text effort.
So I tried this, and it worked, but slightly differently than what the manual suggests.
1 - Press and hold the 2 DPF buttons simultaneously and turn power ON.
2 - Indeed, "A" was displayed, followed by "b", "c", "d" (yes, my capitalization is correct) with each press of parked regen.
3 - when it was displaying "b", I pressed and held the parked regen and the system emitted a loud BEEP and displayed "PUSH". Well <ahem> that's not very informative as to what it wants me to do. Sweet baby Kubota, I love ya, but I aint pushing ya, that's for sure!
At this point I tried pressing the parked regen again, and nothing. Then I cycled the power and the code reappeared. I repeated this whole process several times with various guesses at what the pooter meant by "PUSH" until I tried simultaneously pushing the DPF and parked regen buttons which caused it to display "EXIT". Uh oh, that looked frightening. So I once again cycled power, and the code was now gone.
So, apparently the required steps are 1) press and hold both buttons while turning power on and look for "A". Press parked regen to get it to display "b". Then press and HOLD parked regen until it beeps (quite loud beep, startled me first time) and it should display "PUSH". Press both DPF buttons simultaneously for 2-3 seconds and it should display "EXIT". Now power off. At this point, you should be able to power on again and the error code should be gone.
Thanks for your detailed help. I hope this helps someone else.....