unit tests hosed after installing memcache on windows

I installed memcache on my windows machine ('cached_model') and am now
getting the following error when I run any of my unit tests:

undefined method `use_transactional_fixtures=' for
Test::Unit::TestCase:Class (NoMethodError)

The root cause of the pproblem seems to originate from this inside my
environment.rb file.
require 'cached_model'. If I remove this line, all is good. Of course
I don't want to do this...

Everything I did originated from this article:
http://nubyonrails.com/articles/2006/08/17/memcached-basics-for-rails

Any ideas?

thanks,
phil