undefined method `require_gem' for main:Object

rake aborted!
undefined method `require_gem' for main:Object
D:/Workspace Aptana/depot/rakefile:4
(See full trace by running task with --trace)

...

  if version = defined?(RAILS_GEM_VERSION) ? RAILS_GEM_VERSION : rails_gem_version
    rails_gem = Gem.cache.search('rails', "=#{version}").first

    if rails_gem
      gem "rails", "=#{version}"
      require rails_gem.full_gem_path + '/lib/initializer'
    else
      STDERR.puts %(Cannot find gem for Rails =#{version}:
  Install the missing gem with 'gem install -v=#{version} rails', or
  change environment.rb to define RAILS_GEM_VERSION with your desired version.
)
      exit 1
    end
  else
    gem "rails"
    require 'initializer'

...