Why spacewalk-clone-by-date command fails with error "IOError: unsupported XML-RPC protocol" ?

Issue

• The spacewalk-clone-by-date command fails,

# spacewalk-clone-by-date --user=username --server=localhost -l rhel-x86_64-server-5 rhel-x86_64-server-5U2 -d 2009-01-19   Password:
Traceback (most recent call last):
  File "/usr/bin/spacewalk-clone-by-date", line 206, in ?
    sys.exit(abs(main() or 0))
  File "/usr/bin/spacewalk-clone-by-date", line 196, in main
    return cloneByDate.main(args)
  File "/usr/share/rhn/utils/cloneByDate.py", line 117, in main
    xmlrpc = RemoteApi(options.server, options.username, options.password)
  File "/usr/share/rhn/utils/cloneByDate.py", line 558, in __init__
    self.client = xmlrpclib.Server(server_url)
  File "/usr/lib64/python2.4/xmlrpclib.py", line 1357, in __init__
    raise IOError, "unsupported XML-RPC protocol"
IOError: unsupported XML-RPC protocol