Media ids must be unique, but the hcart type does not need to be different if they exist in the same pool. When a backup or duplicate request is started, it identifies the robot that the current media resides in or is destined to go, and filters it from there. A VTL and physical library cannot share the same robot id if they are presented to Netbackup (obviously if this is a Falconstor VTL and doing the automated tape caching, then thats a bit different since it does not involve Netbackup).
What are the error codes? Can you provide the bptm logs from the media server that is performing the duplicate? I do not think NDMP backups doing direct copy can perform their own duplications- you'll probably need an alternate read host which would be a media server who can see both the VTL and the physical tape library.
