Unregistering the plug-in may result in total uninstallation of the plug-in
If you unregister the NetBackup server from an existing plug-in, the plug-in may uninstall completely from that server and any of the NetBackup servers that are unregistered.
Reasons:
Connectivity issues during the un-registration of the NetBackup server from the plug-in
The NetBackup servers' services are down.
Fix:
Manually install the plug-in and register all the NetBackup servers again.