DebconfError: (30, 'progress bar cancelled') on 6.06.1

Trying to install Kubuntu 6.06.1 over the top of an existing Fedora Core 5, got 'installer crashed' error with the following info:
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Traceback (most recent call last):
  File "/usr/bin/ubiquity", line 130, in ?
    install(sys.argv[1])
  File "/usr/bin/ubiquity", line 55, in install
    ret = wizard.run()
  File "/usr/lib/python2.4/site-packages/ubiquity/frontend/kde-ui.py", line 308, in run
    self.progress_loop()
  File "/usr/lib/python2.4/site-packages/ubiquity/frontend/kde-ui.py", line 538, in progress_loop
    raise RuntimeError, ("Install failed with exit code %s\n%s" %
RuntimeError: Install failed with exit code 1
Traceback (most recent call last):
  File "/usr/share/ubiquity/install.py", line 1263, in ?
    if install.run():
  File "/usr/share/ubiquity/install.py", line 276, in run
    self.db.progress('INFO', 'ubiquity/install/mounting_source')
  File "/usr/lib/python2.4/site-packages/debconf.py", line 60, in <lambda>
    lambda *args, **kw: self.command(command, *args, **kw))
  File "/usr/lib/python2.4/site-packages/debconf.py", line 96, in command
    raise DebconfError(status, data)
DebconfError: (30, 'progress bar cancelled')
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