Only a Policy with Storage Unit specified as that Disk Storage Unit, with that "On Demand Only" option checked, be able to backup to that Disk Storage Unit.
Thanks,
VM
Few suggestions:
1) If you have multiple NICS on the client and want backups to be routed via a backup interface,
add to bp.conf of Client: REQUIRED_INTERFACE = <BACKUP NIC NAME/IP>
2) If you have multiple Backup NICs on Media Server, add all of them...
If you are running bpmedia -unfreeze -m <Media ID> from any machine other than the Media Server that wrote on the Media, then you should be adding a -h <Media Server name> to the command to make it look like this:
bpmedia -unfreeze -m <Media ID> -h <...