@kickycan,
Sorry to see your cat (and you) is/are distressed. Often it can be a sign of old age (senility or bad kidneys), but there's a ray of hope. Sometimes it can be a sign of a minor kidney problem or dietary issue. have you changed the cat's diet..switching foods. I hope you don't give the cat any dairy products. If you do, then eliminate them yesterday.
One of the first things to do when a litterbox problem happens in an elder cat (besides plugging his butt up) is to get the cat tested by the vet. It could be something harmless or minor. Can be a parasite or something in its physical or dietary environment that is uspetting the cat. Vet will rule this out with blood tests and/or a stool sample (cat..not your's).
[Edit: OK bypassing all this info I wrote...without checking the thread.
Put the litter box back exactly where it was originally. Check and make sure the littlerbox liners are not perfumed or are different in any way. Make sure it's the same litter you had been using. If you haven't already done it, have his diabetes meds checked to see if they're adequate.]
The ramp idea for the litter box is a wise move too.
Something has changed for Rocky..and he votes on those changes with his butt!
lastly, don't feed him anything after 7pm.