see Restoring data issue - #2 by Patch
You have to open the Manager data file in Manager v20.9.89 then in a later version.
- Old datafile from very old version of Manager
- Open datafile in v20.9.89 → works
- Open datafile in current version → works
Note if you do it in the reverse order you get multiple reported errors:
- Old datafile from very old version of Manager
- Open datafile in recent version → Not sql database error
- Open datafile in v20.9.89 → Datafile is from a more recent version Manager error
- Open datafile in current version → now should work