Getting error while registering the RHEL 5.4 system to RHN as "There was some sort of I/O Error: unsupported XML-RPC protocol"

Issue

• Not able to register the system to RHN, getting error while running the command:

#rhnreg_ks --username=<user-name> --passsword=<pass-word>
There was some sort of I/O Error: unsupported XML-RPC protocol

• Also see below error message in /var/log/up2date:

up2date_client.up2dateErrors.SSLCertificateVerifyFailedError: The certificate is expired. Please ensure you have the correct certificate and your system time is correct.

• From the rhn_register output

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 _getConf                                                                                        ig
    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 125, in init_hook
    login_info = up2dateAuth.getLoginInfo(timeout=timeout)
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 219, in getLoginInfo
    login(timeout=timeout)
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 170, in login
    server = rhnserver.RhnServer(timeout=timeout)
  File "/usr/share/rhn/up2date_client/rhnserver.py", line 155, in __init__
    self._server = rpcServer.getServer(timeout=timeout)
  File "/usr/share/rhn/up2date_client/rpcServer.py", line 156, in getServer
    timeout=timeout)
  File "/usr/lib/python2.4/site-packages/rhn/rpclib.py", line 169, in __init__
    self._reset_host_handler_and_type()
  File "/usr/lib/python2.4/site-packages/rhn/rpclib.py", line 315, in _reset_hos                                                                                        t_handler_and_type
    raise IOError, "unsupported XML-RPC protocol"
IOError: unsupported XML-RPC protocol