undefined method `set_page_config' for

[joaofraga]

I'm trying to use the ActiveAdmin Sortable and I'm getting the following error:

undefined method `set_page_config' for Admin::CostumersController:Class

Application trace:

app/admin/costumers.rb:17:in `block in <top (required)>'
app/admin/costumers.rb:2:in `<top (required)>'
config/routes.rb:42:in `block in <top (required)>'
config/routes.rb:1:in `<top (required)>'
This error occurred while loading the following files:
   /Users/nda2/Apps/ts-studio/config/routes.rb
   /Users/nda2/Apps/ts-studio/app/admin/costumers.rb

costumers.rb

# encoding: utf-8
ActiveAdmin.register Costumer, :as => "Cliente" do
  menu :label => "Clientes"

  filter :name

#  index do
#    column "Titulo", :name
#    column "Ordem", :position
#    default_actions
#  end

#  sortable :position, :as => :grid do |resource|
#    div resource.title
#  end

sortable :order do
  column :name
  default_actions
end

  form do |f|
    f.inputs do
      f.input :name
      f.input :position
      f.input :url
    end
    f.buttons
  end
end

My bundle list:

Gems included by the bundle:
  * actionmailer (3.2.1)
  * actionpack (3.2.1)
  * activeadmin (0.4.4 4f25ce3)
  * activeadmin_sortable (0.0.1.pre b95dc47)
  * activemodel (3.2.1)
  * activerecord (3.2.1)
  * activeresource (3.2.1)
  * activesupport (3.2.1)
  * arbre (1.0.0)
  * arel (3.0.2)
  * bcrypt-ruby (3.0.1)
  * bourbon (2.1.1)
  * builder (3.0.0)
  * bundler (1.1.4)
  * ckeditor (3.7.1)
  * cocaine (0.2.1)
  * coffee-rails (3.2.2)
  * coffee-script (2.2.0)
  * coffee-script-source (1.3.3)
  * devise (2.1.2)
  * erubis (2.7.0)
  * execjs (1.4.0)
  * fastercsv (1.5.5)
  * formtastic (2.2.1)
  * friendly_id (4.0.7)
  * has_scope (0.5.1)
  * hike (1.2.1)
  * i18n (0.6.0)
  * inherited_resources (1.3.1)
  * journey (1.0.4)
  * jquery-rails (2.0.2)
  * json (1.7.3)
  * kaminari (0.13.0)
  * kgio (2.7.4)
  * libv8 (3.3.10.4)
  * mail (2.4.4)
  * meta_search (1.1.3)
  * mime-types (1.19)
  * multi_json (1.3.6)
  * mysql2 (0.3.11)
  * orm_adapter (0.3.0)
  * paperclip (3.1.2)
  * polyamorous (0.5.0)
  * polyglot (0.3.3)
  * rack (1.4.1)
  * rack-cache (1.2)
  * rack-ssl (1.3.2)
  * rack-test (0.6.1)
  * rails (3.2.1)
  * railties (3.2.1)
  * raindrops (0.10.0)
  * rake (0.9.2.2)
  * rdoc (3.12)
  * responders (0.9.1)
  * sass (3.1.20)
  * sass-rails (3.2.5)
  * sprockets (2.1.3)
  * therubyracer (0.10.1)
  * thor (0.14.6)
  * tilt (1.3.3)
  * treetop (1.4.10)
  * truncate_html (0.5.5)
  * tzinfo (0.3.33)
  * uglifier (1.2.6)
  * unicorn (4.3.1)
  * warden (1.2.1)