Starting on the NetVault Software Version 8.6.3, it is not possible to do DataCopy of Backup Jobs that are set as Archive in the "Advanced Options" of the Backup job definition.
This decision was made by Development, for compatibility with other products within the Data Protection family.
The Solution is to use a very long Backup Life or downgrade the DataCopy Plugin to a version earlier than the one that comes with the NetVault Backup Software version 8.6.3.