problem while connecting to the server

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 <at> mymachine]~/w/dps% ruby script/server
=> Booting WEBrick...
./script/../config/../vendor/rails/railties/lib/initializer.rb:334:in
`send': undefined method `session=' 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:in `each'
        from ./script/../config/../vendor/rails/railties/lib/
initializer.rb:333:in `initialize_framework_settings'
        from ./script/../config/../vendor/rails/railties/lib/
initializer.rb:330:in `each'
        from ./script/../config/../vendor/rails/railties/lib/
initializer.rb:330:in `initialize_framework_settings'
        from ./script/../config/../vendor/rails/railties/lib/
initializer.rb:100:in `process'
        from ./script/../config/../vendor/rails/railties/lib/
initializer.rb:47:in `send'
        from ./script/../config/../vendor/rails/railties/lib/