If the recovery host is not at the same NetBackup release level as the backup host
Note the following about mixed-level backups and restores:
To restore from a NetBackup 8.x backup
To restore a virtual machine from a backup that a NetBackup 7.x backup host performed, a NetBackup 8.x recovery host is required. You cannot use a NetBackup 7.7.x recovery host to restore a virtual machine that was backed up by a NetBackup 8.x backup host.