I was having the exact same problem with our side-by-side. Our kitchen is over a very cold garage. I noticed this problem right when the temperature was consistently below freezing level. Saw the tip in this forum about using a turkey baster to flush the drain hole with hot water and it worked like a charm! Before I did I turned the refrigerator off and left the door open so I could allow the ice formed on the bottom to melt. Even used a hair dryer for a while to speed up the process. Then heated some water in the microwave and used the baster to flush in the hole. A couple minutes later I could literally hear the water rushing down the drain. Was so glad to see that something had just frozen up along the way and it wasn't a clog. I plan to flush hot water down the drain occasionally to maintain it and prevent a freeze in the future.

After clearing the drain using the turkey baster and lots of hot water to melt the ice plug, I installed one of those aluminum pieces that extends down into the drain hole. The drain just froze up again. At this point, I'm going to try changing out the defrost heater, since the only reason I can think of why this keeps happening is that the heating element is just not getting or staying hot enough in the area of the drain to prevent the freezing. Any further ideas are welcome.