Backup Can't be Started. Plug in the External Files of this Backup

I'm using Windows 10 (x64) on a desktop and I want to use Acronis 2019 to back up my hard disc (C: Drive). I'm trying to backup to a brand new WD SSD. It's an empty drive and I just Formatted it.
I got the error message when I tried to backup. I've tried on another new disc (ASUS) with the same error.
What's the fix?
Thanks
Mike

Backup Can't be Started. Plug in the External Files of this Backup
The message above suggests that this backup task has been run previously and has created backup files, hence it is looking for those files but they are not found on the new, empty drive!
Do a validation for the backup task and click on either Ignore (if offered) or cancel for each message about missing files, then retry the task.
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