xubuntu 12.04.4 alternate fails to upgrade ubuntu 10.04 to xubuntu 12.04

[Marc MOREL]

Wanting to avoid Unity, I wanted to shift from Ubuntu 10.04 installed in 2010 and up-to-date (!) to xubuntu 12.04.4, hoping to keep most of my applications, and my dashboards converted to xfce (?)
So I downloaded an alternate CD, checked the md5 of iso, and burnt it. Booted on Cd and used "check content of CD" (I don't know the exact words, I use french menus/keyboard). The "self check" of physical CD was OK.

Then I rebooted my system from my usual boot, sda1, ubuntu 10.04 updated almost dayly, and executed this:
sudo mkdir -p /media/Xub12044LTS_alt_amd64
sudo mount -o loop ~/Téléchargements/xubuntu-12.04.4-alternate-amd64.iso /media/Xub12044LTS_alt_amd64
gksu "sh /media/Xub12044LTS_alt_amd64/cdromupgrade"

... and it seemed to work for a while
There are several steps of download, and one involves 2323 files. While downloading these 2323, the progress bar stops, the display does not change for a long while and the message under the still progress bar says "Downloading file 1951 of 2323 " , until a listbox of error messages appears, with 2323-1951=372 almost identical messages saying
"Failed to fetch cdrom:[Xubuntu 12.04.4.LTS _Precise Pangolin_ - Release amd64 (20140205.2)]/****.deb Hash Sum Mismatch" ; only the name of the rejected .deb packet changes with every message.

The global Md5 sum of the iso is OK, but among the content of the iso, there could be md5 check files not corresponding to what is fetched...

I tried with an other alternate, xubuntu 12.04.3 , downloaded from Harvard servers. There are less errors, the download freezes after more than 2000 files in 2323, but it fails he same way.

I tried mounting iso files rather than burning : same behaviour.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.