"error while loading shared libraries: libnv6json.so: cannot open shared object file: No such fil (4046642)

Customer tried to upgrade existing NetVault Backup Server to 8.6.1 (from 8.5.3) on Debian Lenny x86 and received the following error message:

Performing upgrade tasks
Upgrading configuration
/usr/netvault/bin/nvconfigupdate: error while loading shared libraries: libnv6json.so: cannot open shared object file:

No such file or directory
Failed to update configuration settings
Post install script failed!

I performed some tests and mimicked the customers installation i.e. installed NVBU 8.5.3 (netvault-R2010FEB03-HALO-LinuxX86-64.tar) 64Bit, making sure that all the libraries were installed:

1. apt-get install ia32-libs lib32nss-mdns
2. ./install
3. ldconfig
4. rm -rf /usr/netvault
5. ./install

This was successful and tested backups.
Then installed NVBU 8.6.1 (netvault-R2011OCT12-JUNO-LinuxX86Hybrid.tar) as an upgrade and failed with the same error as before.