We have the same fridge, we just had the same problem, and followed the instructions found on this website. Probably a clogged drain pipe/tube.
After following these instructions, my husband found a chunk of debris in the tube along with a piece of plastic wire tie that was the probable cause of our issue - here is a copy of what we did last night. (The end of the tube has a little rubbery opening that drips into a pan at the base of the rear of the freezer - the beginning of the tube is behind the grill on the back wall of the freezer, have to put the wire through the grill and into the hole - we put the wire up from the bottom and down from the top to be sure to get the clog)
Remove all the drawers in the freezer - and stack them up.
With the unit switched off and unplugged, undo the fixings on the rear pannel in the freezer (behind the drawers)
Remove it to see the evaporator coils
At the base there should be a channel - and a hole leading to the drain pipe. This needs unblocking wih a thin flexible cable. -net curtain support wire is ideal, and cheap. or use a short length of insulated cable.
Check it comes out at the rear of the unit onto the evaporator container - situated on top ofthe compressor.
Replace everything and switch on.