plugins error

HI,

in my applicaition i want to use automatic sesssion cleaning. i followed the website

http://agilewebdevelopment.com/plugins/limited_sessions

I have download this plugin, then configured session life time in environment.rb like

CGI::Session::ActiveRecordStore::Session.recent_activity_limit = 2.hours. finally i have started my server while i am getting following error /usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:478:in `const_missing': uninitialized constant CGI::Session (NameError)

from /home/manivannan/july1/GenuineTravelsTesting/config/environment.rb:52 from /usr/local/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/initializer.rb:47:in `run' from /home/manivannan/july1/GenuineTravelsTesting/config/environment.rb:17 from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require' from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require' from /usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:496:in `require' from /usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:342:in `new_constants_in' from /usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:496:in `require'

how to solve this