Simpler method is remove all food from freezer and fridge and allow to defrost - than start back up - presto...working fine.
It's the pipe that allows air into the fridge to circulate; is frozen. You can tell its this as the fans dont work when the fridge door is first closed.
I have the same problem, and it will keep happening - dont know a long term fix - maybe some else can help?
Chris, December 2008