This freezing can be caused by some debris in the drain slowing the drain, or it can be caused by a weak fridge compressor, dirty condenser, or refrigerant leak somewhere in the system causing the cooling cycles to run too long and freezing the drain. this is usually accompanied by a "service" or "vacuum condenser" warning flashing between the temp readings in the display. If you have one of these warnings, you are probably in for a big repair, the parts will be covered under a 12 year warranty depending on the age of the unit and only if you use an authorized servicer. If no warning lights are present, you can order a fridge defrost drain heater kit and install it, and that will keep the drain line warm so that it doesn't freeze and back up. the easiest way to defrost that drain is to purchase a small handheld steamer form a drug store and use steam to clear the line. Good luck!