How to solve IOError when yum update ?

Issue

• How to solve IOError when yum update ?

# yum update

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 664, in <lambda>
    conf = property(fget=lambda self: self._getConfig(),
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 253, 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 111, in init_hook
    login_info = up2dateAuth.getLoginInfo()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 217, in getLoginInfo
    login()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 168, in login
    server = rhnserver.RhnServer()
  File "/usr/share/rhn/up2date_client/rhnserver.py", line 149, in __init__
    self._server = rpcServer.getServer()
  File "/usr/share/rhn/up2date_client/rpcServer.py", line 159, in getServer
    password=proxyPassword)
  File "/usr/lib/python2.4/site-packages/rhn/rpclib.py", line 156, in __init__
    raise IOError, "unsupported XML-RPC protocol"
IOError: unsupported XML-RPC protocol