Using factory_girl within a rake task - getting uninitialized constant

I'm guessing that Rails hasn't loaded your models at the point you are requiring the factories. Try this:

require 'factory_girl'

namespace :users do

  desc "Create sample users for use in development" 
  task :create_sample_users => :environment do
    require File.expand_path("spec/factories.rb")
    Factory(:user, :email => "[email protected]")
    Factory(:approved_user, :email => "[email protected]") 
  end

end