Hi Brian,
That message indicates that you are trying to use Excel to import a file that has a format of Header / Detail / Detail (ie a header line on one row, followed by the first detail on a different row.
Excel doesn't support that format (the header fields must be repeated for every row). And I don't believe that Adagio Invoices supports the above Header / Detail / Detail format anyway (like OrderEntry does).
Bruce's comment is right on - to see the expected format, export a batch. Also check out the Help file and the very detailed notes about setting up Import Invoices templates - from the main Help menu, choose Importing Invoices or Items, and near the bottom of that page choose the link to 'Import Invoices - File Format Requirements'. Or the link on our website for
Import Tech Tips.