ActiveAdmin register_page doesn't work in heroku

The app crash when I add the next code (from the Active Admin web page):

ActiveAdmin.register_page "Calendar" do
  content do
    para "Hello World"
  end
end

If I execute the same code at heroku console, it works well. But the web app can't get up with this code. In the logs only shows that the app crash with timeout.

The Dashboard page uses the old ActiveAdmin::Dashboards.build, and I can't get work with ActiveAdmin.register_pagefor the same reason.

I've Active Admin 0.5.1 and Rails 3.2.11