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