thanks for getting back to me.
What I realised is that my local copy of Discourse was version 2.5.0.beta4, whereas my Bitnami image on AWS EC2 was 2.4.3.
I downgraded my local version, ran import scripts for the discussion board, created a backup, which I was then able to upload to my EC2 instance and run 'restore' successfully.
This is obviously the opposite of the advised upgrade, but ultimately, I brought both environments onto the same version and was able to achieve what I wanted, which was to migrate from and old discussion board solution onto a new one.
Thanks for your help