[chef] Chef Solo - Unknown error processing config file with error undefined method `absolute_path' for File:Class

[David Montgomery < >]

Why wil chef solo not run?  I am using ruby 1.9.3

My cookbooks are in

/home/ubuntu/workspace/predictivematch-chef/chef-repo/cookbooks

chef-solo -c /home/ubuntu/workspace/chef-repo/solo.rb -j /home/ubuntu/workspace/chef-repo/roles/local_server.json
[2013-07-25T14:24:36+08:00] FATAL: Unknown error processing config file  with error undefined method `absolute_path' for File:Class

Below is my chef-solo file

root = File.absolute_path(File.dirname(__FILE__))
file_cache_path root

cookbook_path root + '/cookbooks'
data_bag_path root + '/data_bags'

file_cache_path = '/var/chef/cache'
Chef::Config[:file_cache_path]= '/var/chef/cache'