This second option anyway is just a test, as the needed backup is bigger than the amount of space I've available: I've just limited the amount of files and room in my tests, to be able to track down the problem.
The error you are getting is due to the limited drive space you have.

When you request a DB backup BackUp ZC stores a copy of the DB in YOURADMIN/backups. You should check that folder and delete any old DB backup files that you do not need. That might free up enough space on your drive.

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