Hi Steve;

     I wonder if the XML Schema (Import/export template) definition has somehow gotten out-of-step with the DWO's column definition? Can you verify the settings in the XML Pane versus what you see in the Column Specification Pane within the DW Painter?

    The other workaround might be to just recreate the External DWO from scratch (if it's not too complex) and see if that fixes the issue (assuming the DWO definition might be compromised).

    If the above does not solve your issue, I would like to suggest that you open a Support Ticket for this external DWO to XLSX problem. Then export and attach the DWO source to the ticket with some test data so that Appeon can try & recreate the problem.

HTH

Regards ... Chris