Your problem is down to the drain hole in the freezer section being blocked.
As the unit is frost free the defrost water is not runnining away, and trickling down the rear wall onto the floor of freezer then freezing as an ice sheet.
Removal of the rear panel in freezer will give you access to the drain hole.
I would try turning off the freezer for a couple of days,
to allow the ice in drain to melt before removing rear wall panel as the ice behind may be quite thick.
Generally the blue plastic coating from the pipework falls off and blocks drain hole.
Tony Randall Fridge Engineer, January 2008