"it may be that the drain hole has simply choked.."
I have the same model, and possibly the same problem ... though the ice is accumulating on the floor of the freezer rather than in a drip tray. Occasionally, the ice melts (and rolls out on to the floor) so I'd imagine the heater probably *is* working.
But I looked, and couldn't find any signs of a drain hole. So to Greg: Any clues where the drain hole should be ???
Harry, June 2008