yum が失敗し、「[Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403」エラーが発生する

Issue

• yum update が失敗し、以下のエラーが表示されます。

# yum update
Loaded plugins: product-id, refresh-packagekit, rhnplugin, security, subscription-manager  
Updating certificate-based repositories.  
https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/os/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403"  
Trying other mirror.  
Setting up Update Process  
No Packages marked for Update  
# yum install gcc  
Loaded plugins: product-id, refresh-packagekit, rhnplugin, security, subscription-manager  
Updating certificate-based repositories.  
https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/os/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403"  
Trying other mirror.

• yum コマンドが失敗し、「[Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403 Forbidden""」 エラーが発生します。
• RHN Classic にシステムが登録されており、その間はプロキシーが使用されています。パッケージをインストールすると、以下のエラーが発生します。

# yum update
Loaded plugins: product-id, rhnplugin, security
This system is receiving updates from RHN Classic or RHN Satellite.
Setting up Update Process
https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/os/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403"
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: rhel-6-server-rpms. Please verify its path and try again