Joined reports are a special format of Salesforce reports that merges two or more different report types into one report.

These reports are only available in XLSX format. Therefore these reports are only supported in Report Sender Plus. If you are using the free version and setup joined reports during a trial period then you may get this error after your trial expires or you cancel a Plus subscription.

To fix this error sign up for a Plus subscription or switch the report schedule to use a report that is not a joined report.