What does undefined method `session=' for ActionController::Base:Class mean?

Hi,

I’m trying to take a rails project built on gem version 1.2.6 and
upgrade it to 2.0.2. So far, I haven’t changed anything except this
line in the config/environment.rb file …

RAILS_GEM_VERSION = ‘2.0.2’ unless defined? RAILS_GEM_VERSION

when I start the server, I get this error:

[me@mymachine]~/w/dps% ruby script/server
=> Booting WEBrick…
./script/…/config/…/vendor/rails/railties/lib/initializer.rb:334:in
send': undefined methodsession=’ for ActionController::Base:Class
(NoMethodError)
from ./script/…/config/…/vendor/rails/railties/lib/
initializer.rb:334:in initialize_framework_settings' from ./script/../config/../vendor/rails/railties/lib/ initializer.rb:333:ineach’
from ./script/…/config/…/vendor/rails/railties/lib/
initializer.rb:333:in initialize_framework_settings' from ./script/../config/../vendor/rails/railties/lib/ initializer.rb:330:ineach’
from ./script/…/config/…/vendor/rails/railties/lib/
initializer.rb:330:in initialize_framework_settings' from ./script/../config/../vendor/rails/railties/lib/ initializer.rb:100:inprocess’
from ./script/…/config/…/vendor/rails/railties/lib/
initializer.rb:47:in send' from ./script/../config/../vendor/rails/railties/lib/ initializer.rb:47:inrun’
… 11 levels…
from /usr/local/apache2/htdocs/dps/vendor/rails/activesupport/
lib/active_support/dependencies.rb:495:in require' from /usr/local/apache2/htdocs/dps/vendor/rails/railties/lib/ commands/server.rb:39 from script/server:3:inrequire’
from script/server:3

What does it mean and any ideas how to fix/troubleshoot? Thanks, -
Dave