When writing a backup job to SmartDisk 1.5.x, the job fails with a Diagnose Media error saying that the "Requesting NetVault version is too old".
Either the NetVault Backup Server or the Client machine being backed up is running on a version of NVBU that is older than the version supported with SmartDisk 1.5.x.
Upgrade the NetVault Backup Server or the Client machine to at least version 1.6.1.