Same problem with Fisher & Paykel 'ActiveSmart' fridge 18 months old and running with no problem till now.
Repair man jumped to the conclusion that it was the fan and replaced the vertical plane fan in the back of the freezer. No joy! Fridge was only vaguely cool at the bottom, but about 25 deg C everywhere else - freezer was at -11 degrees C. I decided there must be a blockage somewhere, & see your post.
After turning off for 24 hrs it seems to be ok again. At least a litre of water dripped from the drain at the back during the defrost, so I surmise that was quite a large lump of ice somewhere I couldn't see.
Rob, January 2008