I was getting this error.
I changed this line in my application.rb from:
Bundler.require(:default, Rails.env) if defined?(Bundler)
to:
Bundler.require(*Rails.groups(:assets => %w(development test))) if defined?(Bundler)
Also, make sure the files are names something.css.sass NOT something.sass
And one other thing, I had an old compass.rb file in my config directory which isn’t needed in Rails 3.2. Deleting that also solved this problem for me.