Why does yum fail with error "[Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403" ?

Issue

• Yum update with the following error:

  # 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 commands fail with [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 403 Forbidden""

• System is registered to RHN classic and proxy is used in between. Facing the below-mentioned error while installing packages :

  # 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