Why if one dives to a depth of 132 feet underwater with a scuba tank
containing 80% nitrogen and 20% oxygen, death from carbon dioxide
poisoning takes place?

I have never heard that this is the case.  I'm a PADI divemaster, and
I'm working on instructor certification, and we're required to study
quite a bit about dive theory.  At that depth, you would have to be
aware of nitrogen building up in your tissues, requiring you to ascend
slowly and stop at designated depths to offload the excess nitrogen to
avoid decompression sickness, otherwise known as the bends.  Another
problem when diving enriched air (nitrox), which usually contains 32%
to 40% oxygen, is oxygen toxicity.

There is no reason that death from CO2 should necessarily occur when
diving to a depth of 132 feet. There are several conditions which
could lead to CO2 poisoning though.

If the diver is trying to conserve oxygen and hypoventilating, there
may not be sufficient CO2/O2 exchange resulting in a CO2 buildup in
the bloodstream.

The same can occur if the diver has impaired lung function and for
physical reasons cannot breathe adequately.

If the scrubber in the rebreather the diver was using is faulty, there
may be too much CO2 in the breating mix.

See http://www.answers.com/topic/hypercapnia.