Sounds like your drain line is plugged.

Could not find info on your specific unit but should not need it but the beklow is a "I think"

When the unit defrosts the water from the ice on the coils drains down into a funnel like device at the top back of the fresh food section. This then drains down to the tray under the machine.

Remove your kick plate and check that the hose end is not blocked by dust/crud.
If OK
Disassemble the fresh food top back area.
Check that it has not frozen up on you. This can happen if it is not draining fast enough.
Then get a straw or a turkey baster and blow the line to clear it. Some people use a compressor but I would use a low air flow rate. Also sometime warm water in the baster helps. The trick is getting what ever you use to seal to the end of the drain tube/funnel.
Once it is clear pour some 10% bleach solution through the tube. Crud likes to grow in the tube and you want to kill it and flush it out.
Be careful not to overfill the tray at the bottom.

Also a great time to clean/check the compressor coil and fan under the unit.