Microsoft Intereop Excel addin missing

Hi,

I have one network user who can't export from NAV to Excel - a message displays "Cannot load an instance of the following .NET Framework object: assembly Microsoft.office.Interob.Excel, Version=15.0.0.0. Culture=neutral, PublicKeyToken=71e9bce111e9429c.

We're on NAV 2016 CU32 with Office 365.

I've run the setup.exe from the DVD - verified that the Office addin was installed, and also did a "Repair". I did not have the user reboot the workstation (yet).

Also, in my local NAV installation, if I look in Excel File/Options/Add-ins, I see an entry for "Microsoft Dynamics NAV Add-in", with the location of:
file///C:\Program Files (x86)\Microsoft Dynamics NAV\90\RoleTailored Client\Microsoft.Dynamics.Nav.ExcelAddin.vsto|vstolocal

On the user's workstation, that line in her "addins" page does not display. I tried to add the addin (it's not displayed when you click "Manage", "Excel Addins" or "manage","COM Addins", and if I click "Add" on the next page and navigate to that file (Microsoft.Dynamics.Nav.ExcelAddin.vsto), I get an error message
"Microsoft.Office.Nav.ExcelAddin.vsto" is not a valid Office Add-In". I also tried to add "Microsoft.Office.Interop.Excel.dll" with the same result.

I don't know much about .vsto files and how they are "installed", nor do I know that this is the cause of my error.

Has anyone run into this issue, and have a solution short of uninstalling the client and reinstalling?

Thanks

Ron