Well, I think it was my fault.
Probably I forgot to drop the oacs-5-9 database (where I had already installed some packages) before executing the installation scripts.
As a result the installed source didn't contain the extra packages and hence the error during the startup.
I repeated the process and all went well, even if during the upgrade from repository I got some errors complaining about nssock_v4.
Thank You very much for your patience!
Claudio