FC system-config-kickstart problem in FC6

[bat21sl]

Good morning,
I'm trying to setup a kickstart install for FC6 (in powerpc p5 at work and in X86_64 at home environment).
As first step I would like to modify a ks.cfg file using system-config-kickstart but when I run the program it seems to invoke a package manager/installer ( I see a pop up with the text 'Retrieving package informations' ) and after a short while it fails with some yum errors:

Traceback (most recent call last):
File "/usr/share/system-config-kickstart/system-config-kickstart.py", line 80, in ?
kickstartGui.kickstartGui(file)
File "/usr/share/system-config-kickstart/kickstartGui.py", line 158, in __init__
self.packages_class = packages.Packages(xml, self.kickstartData)
File "/usr/share/system-config-kickstart/packages.py", line 143, in __init__
self.y = sckYumBase(pbar)
File "/usr/share/system-config-kickstart/packages.py", line 117, in __init__
self.doRepoSetup()
File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 299, in doRepoSetup
repo.setup(self.conf.cache)
File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 526, in setup
raise Errors.RepoError, ('Cannot open/read repomd.xml file for repository: %s' % self)
yum.Errors.RepoError: Cannot open/read repomd.xml file for repository: core

Obviously my box is connected to the internet and if I run a yum update it works fine.
Am I missing anything or is there a bug?
I tryed to run system-config-kickstart in rhas4 u4 ppc and it worked fine.

Any suggestion will be appreciated
Thanks in advance and best regards
Alberto