cannot update from 13.10 to 14.04

[Luca Ferrari]

Hi all,
the problem is that I get a "No new release found" error when I try to
do a release upgrade.
I've done the following trying to wake up my updater (done as root):

apt-get clean
mv /var/lib/apt/lists /var/lib/apt/lists.29092014
mkdir -p /var/lib/apt/lists/partial
apt-get clean
apt-get update
apt-get clean
apt-get update
apt-get upgrade
do-release-upgrade

bu the answer to do-release-upgrade is always as follows:

Checking for a new Ubuntu release
No new release found

and the following is the information about my system:

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 13.10
Release:        13.10
Codename:       saucy


Any idea?

Thanks,
Luca