Assuming general similarity with U.S. made fridges (where I live) you'll probably find one of two things, although it's unusual for it to happen to two fridges at the same time.
1. Check the drain from the area at the back of the inside of the fridge where the melted ice gathers during the defrost cycle. If it's plugged, it could cause the build up.
2. More likely, though, is the failure of the auto defrost system. Here, the device(s) that defrost the ice are one or more small light bulb looking mechanisms. they are about 1 inch in diameter and probably 6 to 8 inches long. They emit heat to defrost the ice, which then drains to the tray/evaporator under the fridge (be sure to clean this evil smelling collector). It's a reasonably easy job to remove and replace the bulbs, however it could also be a circulating fan, which is also accesible, but difficult to describe, especially not knowing the make of your fridge.
Best of luck!