Catalog conversion error converting PSE 18 to PSE 2021 not same as Feb 2021 post

Doing a conversion of a 2018 PSE catalog to a 2021 PSE catalog, the process shows it complete, then a thumb optimization and then a failure message.  Conversion log shows: "conversion log: Failed since Original Catalog was open. Close older version of Elements Organizer.
conversion log: Conversion Failed"

Older version (2018) was not open.  Task manager shows PSE 2021 as the only app running.

Any suggestions?