Yum fails with [Errno 14] HTTP Error 404: Not Found

Issue

• yum update fails with [Errno 14] HTTP Error 404: Not Found
• yum repolist shows Red Hat repositories with zero packages available
• yum upgrade fails with

Error: Cannot retrieve repository metadata (repomd.xml) for repository: rhel-i386-server-5. Please verify its path and try again

• Fail to install packages

Error: failed to retrieve repodata/filelists.xml.gz from rhel-x86_64-server-5
error was [Errno 14] HTTP Error 404: Not Found
 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

• Installing a package with yum fails with the following errors:

# yum install openmotif
Loaded plugins: rhnplugin, security
kde                       100% |=========================| 2.7 kB    00:00
kde/primary_db            100% |=========================|  95 kB    00:00
http://ftp.heanet.ie/pub/kde-redhat/redhat/5Server/i386/stable/repodata/primary.sqlite.bz2: [Errno -3] Error performing checksum
Trying other mirror.
kde/primary_db            100% |=========================|  95 kB    00:00
http://apt.de.kde-redhat.org/kde-redhat/redhat/5Server/i386/stable/repodata/primary.sqlite.bz2: [Errno 14] HTTP Error 404: Not Found
Trying other mirror.
kde/primary_db            100% |=========================|  95 kB    00:00
http://kdeforge2.unl.edu/kde-redhat/redhat/5Server/i386/stable/repodata/primary.sqlite.bz2: [Errno -3] Error performing checksum
Trying other mirror.
Error: failure: repodata/primary.sqlite.bz2 from kde: [Errno 256] No more mirrors to try.

• System fails to update with following error messages:

Error Downloading Packages:
  kernel-headers-2.6.18-274.17.1.el5.x86_64: failed to retrieve getPackage/kernel-headers-2.6.18-274.17.1.el5.x86_64.rpm from rhel-x86_64-server-5
error was [Errno 14] HTTP Error 404: Not Found
  libxml2-2.6.26-2.1.12.el5_7.2.x86_64: failed to retrieve getPackage/libxml2-2.6.26-2.1.12.el5_7.2.x86_64.rpm from rhel-x86_64-server-5
error was [Errno 14] HTTP Error 404: Not Found
...............................................................................................................

• yum update is failing with

yum update
Loaded plugins: refresh-packagekit, rhnplugin
http://download.virtualbox.org/virtualbox/rpm/fedora/6Workstation/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 :
http://download.virtualbox.org/virtualbox/rpm/fedora/6Workstation/x86_64/repodata/repomd.xml
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: virtualbox. Please verify its path and try again