I had a PROTECT rule on StaffMember which I have removed now, although I am not clear about the effect of this rule on the ability to delete an appointment or not. The access level for the Appointment BO is defined as "Full access". But, I still can't delete an Appointment from a calendar, i.e. the Delete option is not showing in the context menu when I right-click on an appointment in the calendar.
Any other ideas?