500 internal server error in ruby on rails application

Actually i am running the rails application which was developed in rails 1.2.6 but when i was running the application in rails 2.0.2 i got the error as

500 Internal server error

Then i saw the development log ,there its showing A secret is required to generate an integrity hash for cookie session data. Use config.action_controller.session = { :session_key => "_myapp_session", :secret => "some secret phrase of at least 30 characters" } in config/environment.rb

Then i added the follwoing lines in environment.rb file

config.action_controller.session = { :session_key => "_myapp_session", :secret => "some secret phrase of at least 30 characters" }

finally the problem is solved