Presumably, this was fixed long ago, but in the interests of others ....
My problems were that when I installed gem_PATH, it was installed elsewhere for the current GEM_PATH, so it could not be found.
So,
GEM_PATH=/usr/lib/ruby/gems/1.8/ bundle install
did the business by setting the GEM_PATH value to the actual location of the gem folder in which the plug harness was installed.
Chrisw
source share