Microsoft Outlook 365 (Windows Only) ADD-IN ERROR


I have been consistently receiving this ADD-IN ERROR which states: "ADD-IN ERROR This add-in could not be started. Close this dialog to ignore the problem or click "Restart" to try again."

This happens from the following very specific chain of events:

  1. When I open the new email/compose screen
  2. As soon as the screen loads I click on the ADD-IN and click a button on the toolbar associated with the ADD-IN

Microsoft Edge Dev Tools (not OWA) do not catch this error because essentially the new email/compose view is not able to be picked up even when I spam refresh. I can view it in Dev Tools only when I don't receive this error.

Outlook logs are hard to read, but I have found one error that might be a smoking gun: Unable to open volatile key. (0x80070005). This however doesn't have much documentation surrounding it.

Would anyone have insight on this issue, Thanks in advance!!

EDIT: ERROR Error: Uncaught (in promise): : {"status":"failed","error":{"name":"MissingExtendedPermissionsForAPIError","message":"Extended Permission missing for the API call.","code":9047}}

This seems to fire in reference to a manifest addition AppendOnSend Here are the docs on this: Why would this error out when clicking on a ribbon icon?

EDIT 2: Trying to validate the XML used in the addin I receive:

has invalid child element 'ExtendedPermissions'

even though I am following the documentation:

asked on Stack Overflow May 7, 2020 by wsoccorsi • edited Jun 1, 2020 by wsoccorsi

1 Answer


The issue here happened to be with using the Microsoft Preview API. The Add-In will throw this error when you accidentally have AppendOnSend enabled while using a manifest that does not have Preview.

answered on Stack Overflow Jun 2, 2020 by wsoccorsi

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