How to designate Internet Calendar as read only

In Outlook 2010 I have subscribed to an Internet Calendar that is read only on the server end. It is not designated as read only in the Outlook client. A user can add an event to this calendar in Outlook, and it persists in the Outlook view of that calendar, but it does not update the calendar on the server end and generates an error in Outlook.

Is there a way to mark this calendar as read only in Outlook so Outlook does not permit attempts to add events? On the properties dialog of this calendar there is no 'Permissions' tab.