If you are using English language version of Excel, but Windows has locale set to a different language, (French, German, etc), Excel may produce an error "Old format or invalid type library".
Barcode Maker has only been tested in English language versions of Windows, and only English is officially supported. You may be able to get it to work in this situation by installing the Multilingual User Interface Pack on the client PC. Search Microsoft's website for the appropriate pack for your version of Windows. If that does not work, our only solution would be to set up a machine with Windows set to English.