How to Fix the Outlook Error "The form region Apple.DAV.Appointment cannot be opened" – IT Solver Support

This article provides a comprehensive guide to resolving the Microsoft Outlook error: "The form region 'Apple.DAV.Appointment' cannot be opened. The form region manifest contains invalid XML." This issue is commonly caused by a corrupted or orphaned iCloud for Windows add-in. We will walk through the complete removal process, including how to overcome a common follow-up error that requires administrator privileges.

Issue Description

When interacting with calendar items (e.g., dismissing reminders), users encounter an error related to "Apple.DAV.Appointment." After uninstalling the iCloud for Windows software, a remnant add-in may persist in Outlook. Attempting to remove this add-in through the standard options can lead to a second error message: "This add-in is installed for all users on this computer and can only be connected or disconnected by an administrator."

Symptoms

Primary Error: A dialog box stating "The form region 'Apple.DAV.Appointment' cannot be opened."
Secondary Error: A dialog box stating "This add-in is installed for all users..." when trying to remove the iCloud add-in.
Inability to manage iCloud-synced calendar items in Outlook.

Affected Systems

Microsoft Outlook on Windows where the iCloud for Windows application is or has been installed.

Resolution Steps for Orphaned Add-in

This guide focuses on the most common scenario where iCloud has been uninstalled, but the add-in remains. Follow these steps to completely remove it.

Confirm the Initial Error: When you dismiss a calendar reminder, you will see the error below. This confirms the issue is with the iCloud form region.
Attempt to Remove the Add-in: In Outlook, navigate to File Options Add-ins. At the bottom, ensure "COM Add-ins" is selected and click "Go...". You will see the "iCloud Outlook Add-in" in the list.
Identify the Administrator Block: When you select the iCloud add-in and click "Remove," you will likely see the following permission error. This is the key obstacle to resolve.
Do not worry, this is expected behavior. The next step will bypass this restriction.
Run Outlook as an Administrator: To gain the necessary permissions, you must restart Outlook with elevated privileges. First, close Outlook completely.
- In the Windows Start Menu, search for "Outlook."
- Right-click on the Outlook application in the search results.
- Select "Run as administrator."
Successfully Remove the Add-in: With Outlook now running as an administrator, repeat Step 2 to navigate back to the COM Add-ins menu (File Options Add-ins Go...).
- Select the "iCloud Outlook Add-in" from the list.
- Click the "Remove" button. This time, the add-in will be removed successfully without any error.
Restart Outlook Normally: Close the administrator instance of Outlook and re-open it from your standard shortcut. The error will be gone, and your calendar reminders will function correctly.

Additional Information: If iCloud is Still Installed

If you have not uninstalled iCloud for Windows and are seeing the initial error, the application files may be corrupt. Before attempting the removal steps above, try the following:

Repair iCloud: In Windows Settings Apps, find "iCloud," select "Modify," and choose the "Repair" option.
Reinstall iCloud: If a repair does not work, fully uninstall iCloud for Windows, restart your computer, and install the latest version from the Microsoft Store or Apple's website.

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