Nokogiri on Mac: “Symbol not found: _xmlAddChild” How do I fix this?

[Gaaargh]

I have been running Cucumber for my Rails app for quite some time
without problems. Looks like something changed (but I don't know
what), because now Nokogiri does not want to work. Apparently it's
having trouble finding the symbol "_xmlAddChild". Not sure I even know
what that means. Can you point me in the direction of reading material
that can educate me, or suggest a solution?

Here's my error output:

/Users/me/.rvm/rubies/ruby-1.9.3-p0/bin/ruby -S bundle exec cucumber
--profile default
Using the default profile...
dlopen(/Users/me/Sites/myapp/nokogiri/ruby/1.9.1/gems/nokogiri-1.5.0/
lib/nokogiri/nokogiri.bundle, 9): Symbol not found: _xmlAddChild
Referenced from: /Users/me/Sites/myapp/nokogiri/ruby/1.9.1/gems/
nokogiri-1.5.0/lib/nokogiri/nokogiri.bundle
Expected in: flat namespace
in /Users/me/Sites/myapp/nokogiri/ruby/1.9.1/gems/nokogiri-1.5.0/lib/
nokogiri/nokogiri.bundle - /Users/me/Sites/myapp/nokogiri/ruby/1.9.1/
gems/nokogiri-1.5.0/lib/nokogiri/nokogiri.bundle (LoadError)

Here's what I've found online:

http://rubyforge.org/tracker/index.php?func=detail&aid=27256&group_id=494&atid=1971

I tried updating the nokogiri gem alone, and with all other gems. No
luck so far.