...but when I try to import the Holidays calendar using the wizard in File menu, I get the following error in a pop-up window:

"The import could not be completed.

An unknown error has occurred in Outlook."

I've not noticed this before because I hadn't really used Outlook until very recently.  I prefer to use it over Mail, Calendar and Contacts.

This could be linked to the fact that the following menu buttos are available, but 'greyed' out:

On the Home tab:

Open Calendar

Permissions

On the Organize tab:

Scale slider

Open Calendar

Properties

Sync

On the Tools tab:

Out of Office

Public Folders

I include these in case it assists in a response.

I'm using OS X Yosemite version 10.10 and the latest Mac Office update was installed earlier this week.

Thank you.