Why does yum list fails with error message as "AttributeError can't set attribute" in Red Hat Enterprise Linux 5?

Issue

• yum list fails with the error follows in Red Hat Enterprise Linux 5.11 ?

# yum list (with attribute errors)
Loaded plugins: rhnplugin, security
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 309, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 157, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 187, in getOptionsConfig
    self.conf
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 665, in <lambda>
    conf = property(fget=lambda self: self._getConfig(),
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 254, in _getConfig
    self.plugins.run('init')
  File "/usr/lib/python2.4/site-packages/yum/plugins.py", line 179, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/rhnplugin.py", line 144, in init_hook
    repo = RhnRepo(channel)
  File "/usr/lib/yum-plugins/rhnplugin.py", line 219, in __init__
    self.metadata_cookie = 'cookie'
AttributeError: can't set attribute