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Error: Unable to cast COM object of type...

Note: this article refers to early releases of Jet Essentials 2015 Update 1


During the installation of the Jet Excel add-in, Windows can return an error attempting to the setup program:

An unexpected error has occurred:
Unable to cast COM object type 'Microsoft.Office.Interop.Excel.ApplicationClass' to interface type 'Microsoft.Office.Interop.Excel.Application'.  This operation failed because the QueryInterface call on the COM component for the interface with IID '{000208D5-0000-0000-C000-000000000048}' failed due to the following error: Library not registered. SystemInvalidCastException.



This issue is caused when Microsoft Office has been 'downgraded' and an entry for the newer version of Office (which has been removed) remains in the Windows Registry.



Note: this information is intended for system administrators, as it involves making changes to the system registry settings, and should only be attempted by someone familiar with and authorized to make such changes.

A system administrator with authority to make changes to the Windows Registry can search for an extra registry entry under


The administrator can then remove the extra entry for the version of Office that is *no longer installed*

Office 2016: 1.9
Office 2013: 1.8
Office 2010: 1.7

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