[SOLVED] Active admin in Rails 4 throws error "Invalid option key"

Active admin in Rails 4 throws error "Invalid option key"

Rails 4 app working just fine until Active Admin is included (from this thread) in the gemfile.

My Gemfile:

gem 'rails', '4.0.0'
gem 'rails_12factor', group: :production
gem 'pg'
gem 'sass-rails', '~> 4.0.0.rc1'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.0.0'

gem 'activeadmin', github: 'gregbell/active_admin'

gem 'protected_attributes'
gem 'rails-observers'
gem 'actionpack-page_caching'
gem 'actionpack-action_caching'

gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder', '~> 1.2'

group :doc do
  gem 'sdoc', require: false
end

The error is thrown while attempting to start the rails server after a clean bundle install.

/var/lib/gems/1.9.1/gems/actionpack-4.0.0/lib/action_controller/railtie.rb:55:in `block (3 levels) in <class:Railtie>': Invalid option key: page_cache_directory= (RuntimeError)

Any help is greatly appreciated!

Solution