A smelly under counter Fridgemaster fridge!?

The Fridgemaster MTBL 140NG undercounter fridge has worked well for more than 5 years. For the past year or so I have had to empty water out from beneath the salad bin and over the past 2 months there has consistently been a bad smell from the fridge every time I open the door. There has alos been a build up of ice at the back top.

Any idea what the problem(s) may be?