"Add tax rule" doesn’t work

Q: I’m having problem with “Add tax rule” button to work. I’m using WordPress 3.4.1 with chrome but tried it also on Firefox, Safari and Explorer. When I click “Add a new tax rule” the panel doesn’t appear.

A: The problem was generated by the Italian translation for countries. Countries with apostrophe generates an error in admin.php. Edit .po file (in your Jigoshop/Languages folder) and change apostrophes with ‘.