Problem creating snapshot backups

Hi

Having problems getting snapshots working - when I click on Add New Snapshot, the progress gets down to Files: : media then I get the following error:

ERROR: PcLZIP file:media add failed -10: gzip temporary file '/home/mydomain/public_html/wp-content/uploads/snapshots/_backup/1479396748/pclzip-582dcde462ea6.gz' has invalid filesize - should be minimum 18 bytes [code -10]

Any ideas what this means and why it's not working - i'm trying to back up both locally and to a connected dropbox but neither is working.

Simon