I had a fresh install of RH 8.0. I registered machine with up2date --register.
Then run up2date -u. I've got this tracebac:

# locale
LANG=C
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=

# up2date -u

Fetching package list for channel: redhat-linux-i386-8.0...
########################################

Fetching Obsoletes list for channel: redhat-linux-i386-8.0...
########################################

Fetching rpm headers...
Traceback (most recent call last):
  File "/usr/sbin/up2date", line 801, in ?
    main()
  File "/usr/sbin/up2date", line 573, in main
    fullUpdate, dryRun=options.dry_run))
  File "/usr/sbin/up2date", line 737, in batchRun
    batch.run()
  File "/usr/share/rhn/up2date_client/up2dateBatch.py", line 55, in run
    self.__findPackagesToUpdate()
  File "/usr/share/rhn/up2date_client/up2dateBatch.py", line 89, in
__findPackagesToUpdate
    self.availableUpdates = plist.getPackagesToInstall()
  File "/usr/share/rhn/up2date_client/packageList.py", line 258, in
getPackagesToInstall
    result = self.__skipPackages(result)
  File "/usr/share/rhn/up2date_client/packageList.py", line 285, in __skipPackages
    packageList = self.__skipFiles(packageList)
  File "/usr/share/rhn/up2date_client/packageList.py", line 306, in __skipFiles
    ignoreMsgCallback = self.ignoreMsgCallback)
  File "/usr/share/rhn/up2date_client/packageList.py", line 365, in buildHeaderList
    hdr = headerList[pkg]
  File "/usr/share/rhn/up2date_client/headers.py", line 121, in __getitem__
    self.__retrievePackage(item)
  File "/usr/share/rhn/up2date_client/headers.py", line 126, in __retrievePackage
    hdr, sourceType = rpcServer.doCall(rpmSource.psc.headerSource.getHeader, item)
  File "/usr/share/rhn/up2date_client/rpcServer.py", line 107, in doCall
    ret = apply(method, args, kwargs)
  File "/usr/share/rhn/up2date_client/rpmSource.py", line 239, in getHeader
    header = source.getHeader(pkg, progressCallback = progressCallback)
  File "/usr/share/rhn/up2date_client/rpmSource.py", line 666, in getHeader
    fd = self.s.getPackageHeader(channel, filename)
  File "/usr/lib/python2.2/xmlrpclib.py", line 821, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.2/site-packages/rhn/rpclib.py", line 126, in _request
    verbose=self._verbose
  File "/usr/lib/python2.2/site-packages/rhn/transports.py", line 141, in request
    return self.parse_response(fd)
  File "/usr/lib/python2.2/site-packages/rhn/transports.py", line 157, in
parse_response
    p.feed(response)
  File "/usr/lib/python2.2/xmlrpclib.py", line 390, in feed
    self._parser.Parse(data, 0)
xml.parsers.expat.ExpatError: not well-formed (invalid token): line 1, column 0