Yes, I know. You are doing the right thing and a good job.
Let’s try a different strategy.
Can you make a backup successfully without including the uploads?
If so, we can simply take(1) that backup and (2) a separate tar
of the uploads directory and accomplish what you want.
So, please try to just do a backup without the uploads (the middle button below); by selecting that option in the backup window; and post back.
If that fails, we will try to do the database backup manually from the command line which is easy enough and will work, I’m fairly certain (we do this all the time and rarely restore from the UX).
Reference:
Note:
Whatever you decide to do @pauln, please do not destroy your existing VPS running Debian 7.5 and Discourse until you have successfully installed another instance of Discourse (and restored and tested) on your new VPS.