When a user chooses 'Add a Calendar' using the calendar (overlay) federation feature, they have no options to select which kind of calendar to add when the add dialog box displays.
As shown in the screen shot below, since there are no options listed in the Add drop down list, a calendar cannot be added. The problem has been seen after upgrading the client and template to Release 8.5.x.
Options in the Add a Calendar drop down list are missing
Resolving the problem
In one case, resetting the mail file owner within the calendar profile resolved the issue. To do this, simply open the mail file and go to More -> Preferences -> Mail tab -> Basics tab, and hit the change button. Next, select the user's name from the Domino directory. Please note that the user's name will already be listed in the Owner field. Performing the above action will reset his or her calendar profile.