Outlook Shared Mailbox Calendar gets "could not be updated" in Outlook only (not OWA)

Question

We have a shared mailbox set up that we're planning to use to share a calendar of events to all users in our organization. When opening this in OWA, the calendar opens correctly and updates as expected when the managing users add items.

However, when trying to open in Outlook, we get an error that the calendar "could not be updated" as in the attached image.

I've checked to ensure the advanced calendar options are turned on, and the setting for this calendar gives the 'Default' permissions as Reviewer, so everyone should have the ability to fully see any items added to this calendar. Does anyone know what might be the solution for this?

Answer 1

Try disabling cached shared folders;

To disable the caching of all shared folders in Outlook 2010 and later versions, follow these steps:

1. On the File tab, click Account Settings in the Account Settings list.
2. In the Account Settings dialog box, click the E-mail tab and then double-click your Microsoft Exchange Server account.
3. In the Change Account dialog box, click More Settings.
4. In the Microsoft Exchange dialog box, click the Advanced tab.
5. Click to clear the Download shared folders check box.

https://support.microsoft.com/en-us/topic/performance-and-synchronization-problems-when-you-work-with-folders-in-a-secondary-mailbox-in-outlook-d45e5881-3d32-ca00-6338-5962cfc41ea8

Answer 2

GPO/ Reg settings

https://learn.microsoft.com/en-us/outlook/troubleshoot/data-files/by-default-shared-mail-folders-are-downloaded-in-cashed