The error is coming from pdinstall, it first checks for existense of /etc/pdregistry.cfg and then looks for /opt/pdag and /opt/pdshared soft links.

Can get the same error by running the precheck -
pdinstall -precheck

The precheck is failing with the error, if there is no /etc/pdregistry.cfg but the links for /opt/pdag and /opt/pdshared links are present.

As a workaround copy the /etc/pdregistry.cfg from the global to the local zone, the precheck should work after that.

After that the install was still hanging, the install log showed the following -

Installing PBX...
Same version is already installed. Nothing to upgrade for package VRTSpbx
Installation log located here: /var/tmp/installpbx-*.log

Unpacking SYMCnbclt package.
Checking for pre-existing SYMCnbclt package.
Installing SYMCnbclt package.

Checked install trace under /usr/openv/tmp/install_cltpkg_trace.<pid>, it was prompting pkgadd for input -

WARNING: The <VRTSpbx> package "Symantec Private Branch Exchange" is a prerequisite package and is not completely installed.

Do you want to continue with the installation of <SYMCnbclt> [y,n,?]

This was the reason for the hang as it cannot interact with the installer.

The reason for the hang is that VRTSpbx package was installed in all zones during the install
of the client in the global zone. In this case it is crucial that it gets installed in the current zone only as /opt is shared,  so need to create a link from /opt/VRTSpbx to a non-shared location, so each zone gets a non-shared copy of PBX (Note: this only needs to be done if /opt is managed by the global zone).

To resolve the hang -

1. Stop PBX in the global zone

/opt/VRTSpbx/bin/vxpbx_exchanged stop

2. Uninstall PBX in the global zone, which will uninstall it from the global zones and also all non-global zones -

installpbx -u

3. Confirmed in all zones that VRTSpbx was uninstalled

pkginfo VRTSpbx

4. If /opt is managed by global zone, create /var/VRTSpbx and link it to /opt/VRTSpbx

On both global and non-global zones -

mkdir /var/VRTSpbx

Only on global zone -

ln -s /var/VRTSpbx /opt/VRTSpbx

5. Reinstall PBX in the global zone only

(Note: "-z" flag in installpbx allows it to be installed in the current zone.)

installpbx -z -f PBX.tar.gz

6. Modify client_config script so it has "-z" flag for installpbx -

installpbx -z -f PBX.tar.gz

7. Rerun NetBackup install in the non-global zone. It will work now.