Re-installed Firebird (from the same/original superserver download)
and it now works - both using a file copy from a winXP v2.0
installation (while servers stopped) and using GBAK.

The re-install notes that there is an existing installation in the
directory, removes it and then re-adds it. So there was either a
hick-up during the original installation which didn't give any visible
warning, or there is a subtle difference between the scripts when
doing a new install vs and update.

Thanks to all who responded

At least we sorted the changes in the GBAK command

Dr John