lucid 10.04 LTS => Precise 12.04.1 : upgrade doesn't work

I googled and looked into all known issues on ubuntu forums related to distribution upgrade but I can't figure out why a 10.04 LTS server won't detect the last LTS 12.04.1. I guess since 12.04 is a fresh dist, not much is reported for related issues

Here is what I did :

apt-get update

apt-get upgrade

apt-get install update-manager-core

it was already installed so no update for this package.

I checked : /etc/update-manager/release-upgrades

[DEFAULT]
# Default prompting behavior, valid options:
#
#  never  - Never check for a new release.
#  normal - Check to see if a new release is available.  If more than one new

#           release is found, the release upgrader will attempt to upgrade to
#           the release that immediately succeeds the currently-running
#           release.
#  lts    - Check to see if a new LTS release is available.  The upgrader
#           will attempt to upgrade to the first LTS release available after
#           the currently-running one.  Note that this option should not be
#           used if the currently-running release is not itself an LTS
#           release, since in that case the upgrader won't be able to
#           determine if a newer release is available.
Prompt=lts

I also checked my sourcelist before running apt-get : /etc/apt/sources.list

deb http://archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe

deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse
# deb http://landscape.canonical.com/packages/hardy ./
# deb-src http://landscape.canonical.com/packages/hardy ./

and then following Ubuntu guide for Precise upgrade the command below should work :

root@xxxxxxxxx:/etc/apt# do-release-upgrade  -d

Checking for a new ubuntu release
No new release found

I tried without dev release option -d but got the same result

Kernel :

root@xxxxxxxxx:/etc/apt# uname -a
Linux XXXXXXXXX 2.6.32-42-generic #95-Ubuntu SMP Wed Jul 25 15:57:54 UTC 2012 i686 GNU/Linux

Linux Distrib :

root@XXXXXXXXX:/etc# cat lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.04
DISTRIB_CODENAME=lucid
DISTRIB_DESCRIPTION="Ubuntu 10.04.4 LTS"

Source list :

root@XXXXXXXXX:/etc/apt# cat sources.list
deb http://archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe

deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse

So am I missing something ?

The server was accessing outside through a proxy but I grant direct access to this server to avoid any Internet access problem or redirection but no clue...

Any help would be appreciated