terminal, users and groups, update manager

when I digit password, terminal tell:
my user is not in the sudoers file. This incident will be reported
If I go on users and groups, a message tell:
The configuration could not be loaded
You are not allowed to access the system configuration.

All begin by an error message went out after I tried to open and work in update manager:

"Could not initialize the package information

An unresolvable problem occurred while initializing the package information.

Please report this bug against the 'update-manager' package and include the following error message:

'E:Encountered a section with no Package: header, E:Problem with MergeList /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_jaunty_main_binary-i386_Packages, E:La lista dei pacchetti o il file di status non possono essere letti o aperti.'"

Allowing the notes of one of yours (marco), I've found the difficult things upon. Then silence...

If there's someone that can continue the street begun by Marco. Or himself. Help!