undefined method `is_frame?

[spham]

I have try this

browser.link(:id, "aboutButton").click

but have an error.

what's happen ?

/Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:672:in`element_not_found_exception': undefined method `is_frame?' for nil:NilClass (NoMethodError)
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:661:in`execute'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:477:in `click_link'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:697:in`page_load'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:476:in `click_link'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir.rb:336:in`click'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:317:in `instance_eval'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir/scripter.rb:317:in`highlight'
    from /Library/Ruby/Gems/1.8/gems/safariwatir-0.4.0/lib/safariwatir.rb:335:in `click'
    from test.rb:7