yum update on RHEL5 fails with: error was [Errno -1] Header is not complete.

Issue

• After registering a RHEL 5 system, all yum update commands (for any package) fail in the following way:

  [root ~]# yum update
  Loading "rhnplugin" plugin
  Loading "installonlyn" plugin
  Setting up Update Process
  Setting up repositories
  rhel-x86_64-server-5      100% |=========================| 1.4 kB    00:00     
  Reading repository metadata in from local files
  Resolving Dependencies
  --> Populating transaction set with selected packages. Please wait.
  ---> Downloading header for sabayon-apply to pack into transaction set.
  sabayon-apply-2.12.4-9.el 100% |=========================|  601 B    00:00     
  Error: failed to retrieve getPackage/sabayon-apply-2.12.4-9.el5.x86_64.rpm from rhel-x86_64-server-5
  error was [Errno -1] Header is not complete.