NDMP Backup fails with "Child Process died unexpectedly", "Fatal error: Backup Died Unexpectedly" (4047909)

Title: NDMP Backup fails with "Child Process died unexpectedly", "Fatal error: Backup Died Unexpectedly" error and browsing the NDMP Plugin causes a "No licence for NDMP Client plugin" to appear.
Date: Jun 11
Product & Version: NetVault All
OS Version: All
Module & Version: NDMP All
Application version: N/A


Symptoms:
NDMP Backup failed with the following error messages:

"Child Process died unexpectedly"
"Fatal error: Backup Died Unexpectedly.

Also were not able to open the "NDMP Client" Configuration, as a "No licence for NDMP Client plugin" had appeared.
Checked in the .../netvault/db/bkl folder to see if the NDMP license was still listed, as the NDMP Plugin and license was installed in the past and backups were working before.
Unfortunately the NDMP license entry had disappeared for some reason (PLG-1024000), even though the NDMP license could be seen in the NetVault Console - Help - About and NetVault Configurator - License tabs.
Editing an existing NDMP job we could see the NDMP Plugin and Client, but drilling down the NDMP Client after modifying it caused a License error message again.
Re-installing the NDMP Plugin had no effect.