A user grants you Free/Busy permission to their calendar, but when you try to open that users calendar in Microsoft Outlook 2016 for Mac or Outlook for Mac 2011, you receive the following error message:
Outlook cannot open the folder. You do not have permission to open this folder. Contact <user_name> for permission.
Outlook for Mac cannot open another user’s calendar when the user’s Calendar folder permission level is set to Free/Busy. This feature is available only in Outlook 2010 and Outlook 2013 for Windows.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2816258 Calendar permissions differences in Outlook 2007, Outlook 2010 and Outlook 2013
To open a shared calendar in Outlook for Mac, the user must grant you permissions of Reviewer or higher. Or, you can view the user's Free/Busy information by creating a new meeting request and then adding that user in the Scheduling Assistant.