Can't share Tableau Public workbook with others

In the past, I've been able to send a .twbx created with Tableau Public to others as an email attachment and then they can save the workbook to their Tableau Public Profile. However, the person I'm sending it to is getting this error message after she opens the workbook in the Tableau Public app and then tries to save it to her Tableau Public profile:

I don't know why this is happening since it has never happened before and because I have set permissions for the workbook as follows on my Tableau Public Profile:

What's going on? Thanks, in advance, for your help.