uninitialized constant ApplicationController::CanCan (NameError) - ruby-on-rails

Question

My application runs normally on development environment but I am getting the following error when I try to run > rails server -e production
I have searched for this and I found answers about restarting unicorn but I don't have unicorn in my application, what can I do to fix it ?
/app/controllers/application_controller.rb:6:in `<class:ApplicationController>': uninitialized constant ApplicationController::CanCan (NameError)
from /home/dexter/Desktop item/Triton/app/controllers/application_controller.rb:1:in `<top (required)>'
from /var/lib/gems/1.9.1/gems/ckeditor-4.0.4/app/controllers/ckeditor/application_controller.rb:1:in `<top (required)>'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:439:in `block (2 levels) in eager_load!'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `each'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `block in eager_load!'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `each'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `eager_load!'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/application/railties.rb:8:in `each'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/application/railties.rb:8:in `all'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:434:in `eager_load!'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/application/finisher.rb:53:in `block in <module:Finisher>'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `instance_exec'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `run'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:55:in `block in run_initializers'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `each'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `run_initializers'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:136:in `initialize!'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /home/dexter/Desktop item/Triton/config/environment.rb:5:in `<top (required)>'
from /home/dexter/Desktop item/Triton/config.ru:3:in `block in <main>'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `instance_eval'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `initialize'
from /home/dexter/Desktop item/Triton/config.ru:in `new'
from /home/dexter/Desktop item/Triton/config.ru:in `<main>'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `eval'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `parse_file'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:200:in `app'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:46:in `app'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:304:in `wrapped_app'
from /var/lib/gems/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:254:in `start'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:70:in `start'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:55:in `block in <top (required)>'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `tap'
from /var/lib/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
My application controller:
class ApplicationController < ActionController::Base
protect_from_forgery
before_filter :authenticate_user!
rescue_from CanCan::AccessDenied do |exception|
flash[:error] = exception.message
redirect_to root_path
end
private
def stored_location_for(resource_or_scope)
nil
end
def after_sign_in_path_for(resource_or_scope)
'/dashboard'
end
end
Gemfile > just posted the place of CanCan
group :assets do
gem 'cancan'
end

Answer 1

Remove cancan from your assets group in your Gemfile. The assets group are gems that are not to be used in production. Therefore when you run the application in production mode, gems in the assets block will be excluded.