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If you want to import items from another calendar into a shared calendar you can't import from an ics file - this will only import into your personal calendar.
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- Select the calendar you want to import the items from (if it's not a calendar you a;ready already have access to you can import the ics file as a separate calendar)
- Click on the View Menu & then Change View
- Select List View
- Press Ctrl A to select all
- Right click & copy
- Go to the shared calendar & change it to list view as above
- Press Ctrl V to paste the items
- Change view back to Calendar once complete
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