I had something similar happen to me back when I owned my 1990 Olds Cutlass Supreme. I was actually playing the CD player. It just stopped. I could momentarily smell that burnt-electrical smell. That was it. From that point onward, it gave that "ERR" msg whenever I tried to play a CD.
I'd recommend getting a replacement at a salvage-yard. I ended up buying and replacing the CD-component part of the radio (once you take the case apart, the radio/cd player is fairly well modularized -- you can unbolt/unplug and remove the cd part). The company I bought it from had some sort of repair contract from GM. The business I bought it from was called "Audio Entronix" and it was located in Plymouth, Minnesota. I don't remember how much it cost. It wasn't a terrible job by any means. I seem to recall it was a bit of a struggle to get the buttons to line up when I had to put the front of the radio back on -- but it wasn't anything more than 5 minutes of wiggling around.