Can't install or update packages

Hello,

We have 2 servers "Red Hat Enterprise Linux Server release 6.7" :

• Our production server.
• Our pre-production (test) server.

When we run a "yum check-update" on our pre-production server, the task are working good without problem. but, on our production server we got an error message like :

https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/optional/os/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403 Forbidden"
Essai d'un autre miroir.
Erreur : Cannot retrieve repository metadata (repomd.xml) for repository: rhel-6-server-optional-rpms. Please verify its path and try again

For information, we dont use proxies and the configuration files are the same on both servers.

Regards,