This occurs because the AdminHomePage is in a Security Category that you are not able to view. An Admistrator will have to add Content Viewing permission to your Admin Group in order to have you see the content of that page. Alternatively, multiple AdminHomePage pages can be created in different security categories so that subadmins with different Content Viewing permissions can see different admin home pages.

Note that despite this error you can still navigate to any other available tab (such as Constituent360) without having to view the content of that page.