iBook author to pdf file links don't work

Hi,

My students created an iBook using iBooks Author 2.2. When I try to share the book by going to share > export > pdf, the pdf file is created but none of the links work. The links are between chapters/sections of the book. For example, the salmon section has a link to the caddisfly section. When a link is clicked on in the pdf file this message pops up:

If I click on Allow, nothing happens and when the link is clicked on again, the same message pops up.

Any help would be greatly appreciated.

Thanks!