This error is displayed in two cases:
- The user tries to create a private event and invite groups that they cannot access. For example, here I try to invite admins:
To make it work, I would need to change the permission on the Admins group.
- A private event is clicked, but no groups are specified.
Maybe we should improve the event builder form to inform the user that this is an incorrect configuration.
@marvi, is it possible that one of those scenarios happened in your case?