Import of Old backup from 2017

Hi
Hoping someone can help.

I have a need to get the files from an old backup of Manager from 2017, the backup is dated (2017-04-24) and I get the message

‘This business database is not valid
Manager data is stored in SQLite database. However it appears the file you are attempting to open is not a SQLite database.’

I am running the desktop version 21.3.70

How can I get access to these files

Thanks in anticipation

Ian

Have look at the last posts here Opening old files in new version - Manager Forum