I was having the same issue, so I deactivated “All-in-One Event Calendar” because we haven’t started using it yet. Please post once a way to help these plug-ins get along has been found.
I’m going to mark this as resolved because I found Private pages were not working well in other ways, how they kept unnesting after publishing changes. So I found a php script to put in the header to forward all non signed in visitors to a coming soon page. It works for this purpose.
