The “jquery-rails” gem recently removed jQuery UI.
https://github.com/rails/jquery-rails/commit/2fdcdb2633cbc6426d412c050200fc31d14b9a3b
They recommend using the jquery-ui-rails gem.
There is an active pull request (as of this writing) to add that gem as a dependency. However, the developers of ActiveAdmin have stated that they are “locking it down until we officially drop support for Rails 3.0”. The version they are locked to is jquery-rails < 3.0.0.
In the meantime, just modify your Gemfile:
gem “jquery-ui-rails” Not recommended, see @Kevin’s comment below
Or you can downgrade your version of jquery-rails:
gem "jquery-rails", "< 3.0.0"
Or you can pull from their Github master branch. They have applied a temporary fix.
gem "activeadmin", github: "gregbell/active_admin"