Oracle backups failing with status code 636

Oracle backups failing intermittenly with status code 636(read from input socket failed). Few backups are successful and few backups are failing. Has anyone noticed this kind of issue ? Backups are using the appliance.

Oracle client -- Solaris and NetBackup version 7.0

Master server -- Linux and NetBackup version 7.5.0.5

Media server -- 5220 appliance