Boot Error : NameError: uninitialized constant ConfigManager::YAML

Hi,
i followed this link
"https://github.com/clint-tseng/odkbuild/blob/master/README.textile" and i
am getting this error while running "bundle exec shotgun config.ru".

http://127.0.0.1:9393/

Boot Error

Something went wrong while loading config.ru
NameError: uninitialized constant ConfigManager::YAML

./config_manager.rb:7:in load' config.ru:15:in inner_app'
/usr/lib/ruby/gems/1.8/gems/rack-1.3.4/lib/rack/builder.rb:51:in instance_eval' /usr/lib/ruby/gems/1.8/gems/rack-1.3.4/lib/rack/builder.rb:51:in initialize'
config.ru:1:in new' config.ru:1:in inner_app'
/usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:102:in eval' /usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:112:in inner_app'
/usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:102:in assemble_app' /usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:86:in proceed_as_child'
/usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:31:in call!' /usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/loader.rb:18:in call'
/usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/favicon.rb:12:in call' /usr/lib/ruby/gems/1.8/gems/shotgun-0.9/lib/shotgun/static.rb:14:in call'
/usr/lib/ruby/gems/1.8/gems/rack-1.3.4/lib/rack/builder.rb:134:in call' /usr/lib/ruby/gems/1.8/gems/rack-1.3.4/lib/rack/handler/webrick.rb:59:in service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in service' /usr/lib/ruby/1.8/webrick/httpserver.rb:65:in run'
/usr/lib/ruby/1.8/webrick/server.rb:173:in start_thread' /usr/lib/ruby/1.8/webrick/server.rb:162:in start'
/usr/lib/ruby/1.8/webrick/server.rb:162:in start_thread' /usr/lib/ruby/1.8/webrick/server.rb:95:in start'
/usr/lib/ruby/1.8/webrick/server.rb:92:in each' /usr/lib/ruby/1.8/webrick/server.rb:92:in start'
/usr/lib/ruby/1.8/webrick/server.rb:23:in start' /usr/lib/ruby/1.8/webrick/server.rb:82:in start'
/usr/lib/ruby/gems/1.8/gems/rack-1.3.4/lib/rack/handler/webrick.rb:13:in run' /usr/lib/ruby/gems/1.8/gems/shotgun-0.9/bin/shotgun:156 /usr/bin/shotgun:23:in load'
/usr/bin/shotgun:23

Operating System : Ubuntu
Description: Ubuntu 12.04.2 LTS
Release: 12.04
Codename: precise

Could anyone please help me how to slove this issue.

Many Thanks
Naveen