Could not load file or assembly ‘Microsoft.Office.Interop.Outlook, Version= after installation with Office 2016, VSTO and .NET 4.5 RRS feed

  • Question

  • Hello,

    we have developed an Outlook Addin with VSTO 2010 and .NET 4.5. The Addin is basically developed with Office 2007 and PIA 2007 ( are referenced but not embedded. When we install the addin on computers with a different outlook version e.g. 2013 or 2016 vsto automatically uses the respective versions of the interop dlls.

    On one installation at a client with office 2016 he keeps still demanding the interop version even if all the interop are correctly installed into the GAC. I had this problem once but there the user in fact had an old Office 2007 programm installed but this time not. But it is not a fresh Office 2016 installation but the client upgraded from 2007 to 2013 and the to 2016.

    We already repaired Office but the error still persists. 

    Has anyone any idea where to look or what could be wrong. I haven't found anything in the internet on how vsto or office loads the interop dlls and where it looks first.

    Thank you very much

    Best regards,


    Regards Mark

    Friday, December 2, 2016 2:36 PM

All replies

  • Hi,

    To my knowledge, we are unable to upgrade Office2007 to Office2013. We could only uninstall it firstly and then install Office2013.

    I suggest you try to repair VSTO Runtime. If you could not find, you could download it from Visual Studio 2010 Tools for Office Runtime



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    Monday, December 5, 2016 9:04 AM