Description of problem:

During the last phase of the upgrac ('downloading installer metadata...')
an exception is raised. Here is the stack trace:

Traceback (most recent call last):
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 198, in on_assistant_apply
    self._do_main()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 206, in _do_main
    self.main_preupgrade()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 349, in main_preupgrade
    self.pu.retrieve_treeinfo()
  File "/usr/lib/python2.5/site-packages/preupgrade/__init__.py", line 390, in
retrieve_treeinfo
    raise PUError, "Cannot find any kernel/initrd section for this arch in treeinfo"