If it's a model that's meant to defrost, we have a similar problem on our fridge occasionally where the outlet drain at the back of the fridge freezes up and won't let the water drain out. A quick poke around in a drain hole with a knitting pin or something like that could fix the problem? Not sure where any such drain might be on your freezer or if it has such a thing though - just a suggestion.
Drew, May 2011
