But sass-rails was in the assets group of the Gemfile, so was bundler including the gems in the assets group?
Turned out that ActiveAdmin was requiring it. But, because I had it in assets, it wasn't being loaded into my production set of gems. Solution - move it out of assets. This was listed in the active_admin documentation, here, but I skimmed right past it -- assuming that the Gemfile would save me.
One more problem: I couldn't install bcrypt-ruby and couldn't do sudo. So I tried this in the Gemfile:
gem 'bcrypt-ruby', :require => 'bcrypt'I picked this idea up from here: http://stackoverflow.com/a/3901165