With admin activation enabled, an admin can force a user to reactive his account which sends an email to the user with an activation link. However, if the account hasn't been activated by an admin yet, the link isn't working and displays "You do not have the necessary permissions to complete this operation." to the user.

Ideally, "Force reactivation" for a user shouldn't be possible if admin activation is enabled and the account hasn't been activated by an admin yet.