COM Interop.Excel and Interop.Word 0x80029C4A 오류시

After installing my application (the installation log looks fine), a particular client (US Military) received the following error when trying to start my application:

 

System.InvalidCastException: Unable to cast COM object of type 'Microsoft.Office.Interop.Word.ApplicationClass' to interface type 'Microsoft.Office.Interop.Word._Application'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00020970-0000-0000-C000-000000000046}' failed due to the following error: Error loading type library/DLL. (Exception from HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY)).

 

Based on other responses I have read on this error, it looks like the registry may be corrupted by Anti-virus script blocking software or by multiple instances of Office installed.  Indeed the client is running the Symantec software. Are there other causes I should be aware of?

 

Is there something my code can do to get around this?  I don’t want to have them reinstall Office, as to them it is working fine (i.e. they can start Word and Outlook manually just fine).