Active Admin is a gem used for having an admin dashboard in your application. It uses Devise for logging in users and creates a separate admin_user model for th
admin_user
Why are you using the get "/"? You should remove it. I'm using a definition pretty similar to yours and works fine with me. Use just:
get "/"
root :to => 'users#dashboard', :constraints => lambda {|r| r.env["warden"].authenticate? } root :to => 'home#index'