I have an external user who logs in to my SharePoint with an internal Domain user. When he tries to open an Excel file from a document library Excel opens and a login screen appears inside the workbook.

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When the user types in the internal username and password nothing happens.

Does anyone had the same Problem and a solution or tip for me?



The user informed me that this issue appears after he reinstalled his Windows and switched to Office 2016.


I found a Support page from Mircosoft Germany about the differences between Office 2016 32-Bit and 64-Bit Version. They write that there is a Limitation in the 64-Bit Version regarding the usage of the ActiveX-Control-Library.

It may be possible that the Login Screen uses ActiveX-Controls and the user has installed Office 2016 64-Bit Version. So it cannot work, I suggest?

Here is the link to the German article: https://support.office.com/de-de/article/Ausw%C3%A4hlen-der-64-Bit-oder-32-Bit-Version-von-Office-2016-2dee7807-8f95-4d0c-b5fe-6c6f49b8d261

This may be the same in English: https://support.office.com/en-us/article/Choose-the-64-bit-or-32-bit-version-of-Office-2016-2dee7807-8f95-4d0c-b5fe-6c6f49b8d261?CorrelationId=ba85d154-d322-4fff-aaf7-98184babdb29&ui=en-US&rs=en-US&ad=US

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