Problem with watir-webdriver

facebook.rb

# Ruby 1.9.3-p194 on Windows 7

require 'watir-webdriver'

browser = Watir::Browser.new
browser.goto 'http://www.facebook.com'

# Result

c:/usr/lib/ruby/gems/1.9.1/gems/childprocess-0.3.2/lib/childprocess/windows/lib.rb:284:in
`handle_for': The segment is already unlocked. (158) (ChildProcess::Error)
        from c:/usr/lib/ruby/gems/1.9.1/gems/childprocess-0.3.2/lib/childprocess/windows/l
ib.rb:242:in `dont_inherit'
        from c:/usr/lib/ruby/gems/1.9.1/gems/childprocess-0.3.2/lib/childprocess.rb:154:in
 `close_on_exec'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/firefox/socket_lock.rb:46:in `can_lock?'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/firefox/socket_lock.rb:31:in `lock'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/firefox/socket_lock.rb:17:in `locked'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/firefox/launcher.rb:32:in `launch'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/firefox/bridge.rb:19:in `initialize'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/common/driver.rb:31:in `new'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver/common/driver.rb:31:in `for'
        from c:/usr/lib/ruby/gems/1.9.1/gems/selenium-webdriver-2.22.2/lib/selenium/webdri
ver.rb:65:in `for'
        from c:/usr/lib/ruby/gems/1.9.1/gems/watir-webdriver-0.6.1/lib/watir-webdriver/bro
wser.rb:35:in `initialize'
        from facebook.rb:6:in `new'
        from facebook.rb:6:in `<main>'