ActiveShipping throwing error in build_access_request

I'm using ActiveShipping to try and query for shipping rates - and
when I'm getting an error when it's building xmlnode.

The full code calls and the stack trace are here:

http://pastie.org/226833

but here are snippets:

result = ups.find_rates(origin, destination, packages)

NameError (undefined local variable or method `transitive' for
<UNDEFINED> ... </>:REXML::Document):
    /opt/local/lib/ruby/1.8/rexml/document.rb:186:in `write'
    /vendor/plugins/active_shipping/lib/vendor/xml_node/lib/
xml_node.rb:216:in `to_xml'
    /vendor/plugins/active_shipping/lib/active_shipping/shipping/
carriers/ups.rb:94:in `build_access_request'
    /vendor/plugins/active_shipping/lib/active_shipping/shipping/
carriers/ups.rb:80:in `find_rates'