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This issue occurs if the Group similar folders, such as Inboxes, from different accounts check box is selected and the Hide On My Computer folders check box is cleared in General Preferences.
![Screen shot showing that the "Group similar folders, such as Inboxes, from different accounts" check box is selected and the "Hide On My Computer folders" check box is cleared Screen shot showing that the "Group similar folders, such as Inboxes, from different accounts" check box is selected and the "Hide On My Computer folders" check box is cleared](https://support.microsoft.com/Library/Images/3007333.png)
To resolve this issue, in Outlook 2016 for Mac, click on Outlook, then Preferences, then General. Check the box "Hide On My Computer folders" and close the preferences. The Calendar permissions button will now be clickable.