Your organization's policies don't allow you to share with these users. Go to External Sharing in the Office 365 admin center to enable it

All of a sudden, we are getting the message "Your organization's policies don't allow you to share with these users. Go to External Sharing in the Office 365 admin center to enable it" when adding someone outside the organization to the alerts.  The site is shared, I know this because everyone outside the organization are able to download files, upload files none of that has changed but try adding someone outside to the alerts email group, it halts right there.  I've included 2 screen shots of my dilemma, anyone have an answer I'd be much obliged.