Rails isn't showing you the proper error due to the issue found here: https://github.com/rails/rails/issues/10559
Try formatting the devise_for statement like this:
devise_for :users, {
class_name: 'User',
module: :devise,
controllers: {
registrations: 'users/registrations',
sessions: 'users/sessions',
passwords: 'users/passwords'
}
}
It looks like your devise.rb file was generated by an older version of the gem. Try deleting devise.rb and running rails g devise:install