Hi,
this error message means that JabRef cannot find an entry for the given ISBN. JabRef tries two websites to find information about ISBN (GVK and open library) and it seems like they don’t have any data for this ISBN. In this case you can try e.g. Online ISBN to BibTeX converter - BibTeX.com and paste the bibtex on the main table.
In the latest development version, we have improved the error messages already to be more user-friendly.