未初始化的常量Sass :: Plugin（NameError） - 没有一个解决方案对我有用

Question

我的Gemfile：

source "http://rubygems.org"

ruby "1.9.3"

gem "rails", "3.2.5"
gem "mysql2", "~> 0.2.17"
gem "to_xls"
gem "monkeywrench"
gem "activeadmin" #, "~> 0.6.0"
gem "prawn"
gem "gocardless"

# gem 'jquery-rails'

group :assets do
  gem 'uglifier', '>= 1.2.4'
  # gem 'bootstrap-sass', '~> 2.0.3.1'
  gem 'sass-rails',   '~> 3.2.3'
  gem 'coffee-rails', '~> 3.2.1'
  gem 'therubyracer'
end

group :test do
  gem "capybara", "~> 1.1.4"
  gem "rspec-rails"
end

错误：

/Users/alex/.rvm/gems/ruby-1.9.3-p547/gems/activeadmin-0.6.3/lib/active_admin/application.rb:249:in `generate_stylesheets': uninitialized constant Sass::Plugin (NameError)
    from /Users/alex/.rvm/gems/ruby-1.9.3-p547/gems/activeadmin-0.6.3/lib/active_admin/application.rb:110:in `prepare!'
.....

我找到了一些解决方案，但没有一个解决方案。

#application.rb 

#.....
    config.filter_parameters += [:password]
    # ActionController::Base.config.relative_url_root = ''
    config.sass.preferred_syntax = :sass
  end