Unable to gather data for some mailboxes

Cause:

Insufficient permissions to access room mailbox calendar.

Resolution:

• Ensure that the user provided in Organization Settings page has Calendar access permission on required room mailboxes.
• If not, run the following commandlet in Exchange Management Shell:
  
  Get-Mailbox -RecipientTypeDetails 'RoomMailbox' | Foreach-Object {Add-MailboxFolderPermission $_":\Calendar" -User <user n Org settings page> -AccessRights Reviewer}