Impossible to upgrade from 12.04 LTS to 14.04 LTS

[AlainKnaff]

Just tried to upgrade a 12.04 installation to 14.04 using do-release-upgrade

do-release-upgrade just says "No new release found"

According to https://wiki.ubuntu.com/Releases, 12.04 is still supposed to be supported until April 2017, so don't tell me I'm way too late to upgrade.

root@lll:~# lsb_release -rd
Description: Ubuntu 12.04.5 LTS
Release: 12.04
root@lll:~# apt-cache policy update-manager-core
update-manager-core:
  Installed: 1:0.156.14.19
  Candidate: 1:0.156.14.19
  Version table:
 *** 1:0.156.14.19 0
        500 http://be.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.156.14.5 0
        500 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 Packages
     1:0.156.14 0
        500 http://be.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

What you expected to happen:
- Until April 2017 (at least), it should still be possible to upgrade from 12.04 to 14.04

What happened instead
- do-release-upgrade tells me No new release found