rake assets precompile failure

_helpers.scss

/* ==========================================================================
 * Helper classes
 * ========================================================================== */
//@import "variables";
/*  Image replacement */
.ir {
  background-color: transparent;
  border: 0;
  overflow: hidden;
  /* IE 6/7 fallback */
  *text-indent: -9999px;
}

.ir:before {
  content: "";
  display: block;
  width: 0;
  height: 150%;
}

.fr {
  float: right;
}
/* .... */

application.css.scss

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
 * or vendor/assets/stylesheets of plugins, if any, can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any styles
 * defined in the other CSS/SCSS files in this directory. It is generally better to create a new
 * file per style scope.
 *
 *= require_tree .
 *= require_self
 */
@import "variables";
@import "mixins";
@import "grids";
@import "fonts";
@import "h5bp";

application.rb

require File.expand_path('../boot', __FILE__)

require 'rails/all'

# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)

module Vitabiotics
  class Application < Rails::Application
    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration should go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded.

    # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
    # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
    # config.time_zone = 'Central Time (US & Canada)'

    # The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
    # config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
    # config.i18n.default_locale = :de
    config.generators { |g| g.assets false }
    # Precompile all assets except those with underscore
    config.assets.precompile << /(^[^_\/]|\/[^_])[^\/]*$/
  end
end

paddlefoot.scss

/*
 A lot of SCSS code here
*/
@import "helpers";