I'm trying to edit the permissions on a shared calendar to give "delegate" permission to the calendar, and to remove an old entry from the list of users. Neither change will save, I get an error that says "modified permissions could not be saved". I tried sending an invite to the calendar and it switched permissions for that user to "custom" and they can view but still can't add or edit as "delegate" would, which is what we need. On a brand new, blank calendar, there are no permission issues but it would not allow me to copy and paste all the entries from the old calendar into the new one (and this is not an ideal solution anyway, just a band-aid). This is a hybrid environment w on-prem Exchange and Office 365 syncing. It's very important we get this working asap and any help would be greatly appreciated. Thanks in advance.