[CentOS] Error in updating to 5.7

Hi all,

I have a Dell server, CentOS 5.6 64 bits, on which I configured the CR 
repository. I just tried to update to 5.7, and had this error :
# yum update
....
http://mirror.centos.org/centos/5/cr/x86_64/repodata/filelists.sqlite.bz2: 
[Errno 14] HTTP Error 404: Not Found
Trying other mirror.
Error: failure: repodata/filelists.sqlite.bz2 from cr: [Errno 256] No 
more mirrors to try.
  You could try using --skip-broken to work around the problem
  You could try running: package-cleanup --problems
                         package-cleanup --dupes
                         rpm -Va --nofiles --nodigest
The program package-cleanup is found in the yum-utils package.

My repolist is this one :
# yum repolist
Loaded plugins: dellsysid, fastestmirror, refresh-updatesd
Loading mirror speeds from cached hostfile
  * addons: distrib-coffee.ipsl.jussieu.fr
  * base: distrib-coffee.ipsl.jussieu.fr
  * epel: fr2.rpmfind.net
  * extras: centos.crazyfrogs.org
  * updates: centos.crazyfrogs.org
repo id                               repo 
name                                                         status
addons                                CentOS-5 - 
Addons                                                 enabled:    0
base                                  CentOS-5 - 
Base                                                   enabled: 3535
cr                                    CentOS-5 - 
CR                                                     enabled:  573
dell-omsa-indep                       Dell OMSA repository - Hardware 
independent                       enabled:  719
dell-omsa-specific                    Dell OMSA repository - Hardware 
specific                          enabled:    2
epel                                  Extra Packages for Enterprise 
Linux 5 - x86_64                    enabled: 6700
extras                                CentOS-5 - 
Extras                                                 enabled:  233
updates                               CentOS-5 - 
Updates                                                enabled:  150
repolist: 11912

Other information :
# cat /etc/redhat-release
CentOS release 5.6 (Final)
# uname -a
Linux xxxxxxx 2.6.18-274.el5 #1 SMP Fri Jul 22 04:43:29 EDT 2011 x86_64 
x86_64 x86_64 GNU/Linux

Does anybody has an idea why I have this error ?

Thanks for the help.

-- 
==========================================================
Alain Péan - LPP/CNRS
Administrateur Système/Réseau
Laboratoire de Physique des Plasmas - UMR 7648
Observatoire de Saint-Maur
4, av de Neptune, Bat. A
94100 Saint-Maur des Fossés
Tel : 01-45-11-42-39 - Fax : 01-48-89-44-33
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