Сбой программного обеспечения в Ubuntu 12.10

У меня проблема с Ubuntu Software Center. Когда я его открываю, он автоматически закрывается без каких-либо разрешений. Когда я запускаю его в терминале, я получаю следующее:

vangjush@vangjush:~$ software-center
2013-05-06 21:41:29,532 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None'
2013-05-06 21:41:29,540 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True
2013-05-06 21:41:30,052 - softwarecenter.backend.reviews - WARNING - Could not get usefulness from server, no username in config file
2013-05-06 21:41:30,061 - softwarecenter.fixme - WARNING - logs to the root logger: '('/usr/lib/python2.7/dist-packages/gi/importer.py', 51, 'find_module')'
2013-05-06 21:41:30,061 - root - ERROR - Could not find any typelib for LaunchpadIntegration
2013-05-06 21:41:30,217 - softwarecenter.ui.gtk3.app - INFO - show_available_packages: search_text is '', app is None.
2013-05-06 21:41:30,555 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open()
Traceback (most recent call last):
  File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 257, in open
    self._cache = apt.Cache(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 102, in __init__
    self.open(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 149, in open
    self._list.read_main_list()
SystemError: E:Malformed line 57 in source list /etc/apt/sources.list (dist parse)
2013-05-06 21:41:31,504 - softwarecenter.db.enquire - ERROR - _get_estimate_nr_apps_and_nr_pkgs failed
Traceback (most recent call last):
  File "/usr/share/software-center/softwarecenter/db/enquire.py", line 115, in _get_estimate_nr_apps_and_nr_pkgs
    tmp_matches = enquire.get_mset(0, len(self.db), None, xfilter)
  File "/usr/share/software-center/softwarecenter/db/appfilter.py", line 89, in __call__
    if (not pkgname in self.cache and
  File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 277, in __contains__
    return self._cache.__contains__(k)
AttributeError: 'NoneType' object has no attribute '__contains__'
Traceback (most recent call last):
  File "/usr/bin/software-center", line 182, in <module>
    app.run(args)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 1387, in run
    self.show_available_packages(args)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 1325, in show_available_packages
    self.view_manager.set_active_view(ViewPages.AVAILABLE)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/session/viewmanager.py", line 151, in set_active_view
    view_widget.init_view()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/availablepane.py", line 173, in init_view
    self.cache, self.db, self.icons, self.apps_filter)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/lobbyview.py", line 80, in __init__
    self.build()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/lobbyview.py", line 324, in build
    self._build_homepage_view()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/lobbyview.py", line 119, in _build_homepage_view
    self._append_whats_new()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/lobbyview.py", line 253, in _append_whats_new
    whats_new_cat = self._update_whats_new_content()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/lobbyview.py", line 238, in _update_whats_new_content
    docs = whats_new_cat.get_documents(self.db)
  File "/usr/share/software-center/softwarecenter/db/categories.py", line 131, in get_documents
    nonblocking_load=False)
  File "/usr/share/software-center/softwarecenter/db/enquire.py", line 330, in set_query
    self._blocking_perform_search()
  File "/usr/share/software-center/softwarecenter/db/enquire.py", line 225, in _blocking_perform_search
    matches = enquire.get_mset(0, self.limit, None, xfilter)
  File "/usr/share/software-center/softwarecenter/db/appfilter.py", line 89, in __call__
    if (not pkgname in self.cache and
  File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 277, in __contains__
    return self._cache.__contains__(k)
AttributeError: 'NoneType' object has no attribute '__contains__'

Что случилось? Как это исправить?