i've followed instructions from the installation manual
basically you must create a nsh-install-defaults file with the options you want to install, then send it to the /tmp of the target machine along with the agent package and you launch it with the -silent option
so far the upgrade process works better on the unix platforms (on which we never had a single failure) than on windows (which by contrast has a carnival of possible failures)
Running it with only -silent solves the problem.
Now I've created a BLPackage to deploy the update using BL...update goes successfull, but as agent is restarted automatically after installation, for configuration manager job remain in status running....
use the file deploy job method as specified in the 'bladelogicinstallation.pdf'