just_add_watir

A. Make sure you prefix your element with the correct frame reference …
Example watir:

@b.goto('http://justaddwatir.com/watir/test_html/tc_0001_0100/test_0017.html')
@b.frame(:index, 2).button(:name, "submit").click

Note: sometimes frames aren’t easily identified with id or name attributes, the example above uses the index attribute to get to the second frame in the frameset.