I have the same problem, just found out today that all you need to do is buy a fan motor. Your fan motor is not blowing the cold air up through the fridge hense the bottom 2 compartments are freezing up. Cost of this part is 18.99 + carriage from becospares.co.uk. Should be able to fix yourself, you will find the fan motor behind the panel at the back of the fridge.
Apollo Creed, September 2010