I have been trying to better organize information in my workplace by uploading various users' exchange calendars to a public webpage. SharePoint has potentially useful calendar overlay integration with Outlook; however, it doesn't seem like it's possible to sync multiple Outlook calendars to a master SharePoint online calendar. I'm a rookie in the SharePoint world, so I might be missing something.

So far, I am able to connect the calendar to Outlook desktop client, but not visa versa, so calendars are not visible to the public webpage. Using the "Calendar Overlay," I am able to connect an Exchange calendar, but it gives me the following error when trying to load the calendar:

The HTTP request is unauthorized with client authentication scheme 'Ntlm'. The authentication header received from the server was 'Basic Realm="".(8d4bc19e-809d-8000-e01b2c302846e9e1-8000-e01b-2c302846e9e1)

I have also provided the error in image as seen below:


Research on the site and others leads me to believe that this sort of integration isn't supported by SharePoint. Am I approaching this the wrong way? I was really excited to use this overlay capability, but I'm starting to doubt this is possible.

1 Answer 1


The error "The HTTP request is unauthorized with client authentication scheme 'Ntlm'" occurs because the ability to use the calendar overlay in a SharePoint Online or SharePoint Server calendar that is retrieved from Exchange Online isn't supported. We cannot use the calendar overlay to let the Exchange Online calendar display in the SharePoint Online.

For more information, please refer to this KB article.

As a workaround, you may need to create your own customization calendar solution or use the third-party tool.

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