When attempting to run: 

    railroad -C | neato -Tpng > ~/Desktop/controller.png

I get errors as follows:

    Error loading controller classes.
    (Are you running railroad on the aplication's root directory?)

    /opt/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in 
    `gem_original_require': no such file to load -- xml_simple 
    (MissingSourceFile)

The model XmlSimple is a part of Rails ActiveSupport (installed locally under vendor/rails)

How do we resolve this?