"cross-thread violation on rb_gc" when calling watir-webdriver via irb

i googled "cross-thread violation on rb_gc" and came across a ton of posts that were related, but not quite what i was experiencing.  in fact, i didn't find a post addressing cross-thread errors when calling watir-webdriver via irb, but found this: http://carol-nichols.com/2010/12/bug-cross-thread-violation-on-rb_gc

i uninstalled json and tah-dah!  cross-thread errors are gone!  thanks carol!  hopefully, i won't need json anytime soon otherwise i might have just created an even bigger problem for myself.  heh!

UPDATE:
if you reinstall json it still works.  just tried calling watir-webdriver in irb w/out errors.  w00t!