When you open PS21, click on  Import-> Client Data Conversion->Submit Client Data for Conversion.  Then, you click through the wizard until you get to the window that says "Ultra Tax CS Software Conversion File Back Up Instructions."  The error is in those instructions.  It also appears on the website here...  https://proconnect.intuit.com/community/form-1040/help/ultratax-cs-backup-instructions-for-data-conv...  These might be correct instructions for converting 2019 to 2020, but they won't work for 2020 to 2021 conversions.