3D FlipBook - When I try to add a pdf what appears is “Please wait! The book is processing…” and stay there indefinitely, doesn’t

When I try to add a pdf what appears is “Please wait! The book is processing…” and stay there indefinitely, doesn’t load the book or anything. I have been using your free version and it was working fine, so I just purchased your PRO version but zip file will not import into my plugins. It comes back with ‘The link you followed has expired.’ I care less about that right now than getting my PDF installed.