Comment 3 for bug 847475

The root cause of the error is
Sep 11 20:11:55 ubuntu ubiquity: Traceback (most recent call last):
Sep 11 20:11:55 ubuntu ubiquity: File "/usr/bin/apt-clone", line 113, in <module>
Sep 11 20:11:55 ubuntu ubiquity: args.source, args.destination, args.new_distro_codename, protect_installed)
Sep 11 20:11:55 ubuntu ubiquity: File "/usr/lib/python2.7/dist-packages/apt_clone.py", line 305, in restore_state
Sep 11 20:11:55 ubuntu ubiquity: self._restore_package_selection(statefile, targetdir, protect_installed)
Sep 11 20:11:55 ubuntu ubiquity: File "/usr/lib/python2.7/dist-packages/apt_clone.py", line 426, in _restore_package_selection
Sep 11 20:11:55 ubuntu ubiquity: self._restore_package_selection_in_cache(statefile, cache, protect_installed)
Sep 11 20:11:55 ubuntu ubiquity: File "/usr/lib/python2.7/dist-packages/apt_clone.py", line 406, in _restore_package_selection_in_cache
Sep 11 20:11:55 ubuntu ubiquity: resolver.resolve()
Sep 11 20:11:55 ubuntu ubiquity: SystemError: E:Unable to correct problems, you have held broken packages.

Which is caused by
Sep 11 20:05:31 ubuntu ubiquity: WARNING:root:can't add at-spi (pkg at-spi not marked upgrade)
(bug 836798?)

This situation should handled more nicely than a python traceback