Consider the following scenario:
- You have a calendar overlay in Microsoft SharePoint Online.
- You configure the calendar overlay to do the following:
- Retrieve a calendar from Microsoft Exchange Online
- Display the calendar within the SharePoint Online calendar
The HTTP request is unauthorized with client authentication scheme 'Ntlm'. The authentication header received from the server was 'Basic Realm=""'.
This issue occurs because the ability to use the calendar overlay in a SharePoint Online calendar that is retrieved from Exchange Online isn't supported.
Article ID: 2997170 - Last Review: Dec 20, 2016 - Revision: 1
Microsoft SharePoint Online, Microsoft Exchange Online