Upgrades from NetBackup 7.6.0.4 and earlier are not supported
Substantial logic is required to upgrade NetBackup from release to release. In the interest of efficiency, upgrade logic specific to NetBackup 7.6.0.4 and earlier is retired. These releases of NetBackup are end of support life and are unsupported. If you attempt to upgrade NetBackup 7.6.0.4 or earlier to 8.1.2, the preinstallation check fails and the upgrade cannot continue.
If you are running one of these versions of NetBackup and want to upgrade to NetBackup 8.1.2, use an intermediate release as a stepping stone. More information is available about supported versions of NetBackup