I'm having a problem with Ubuntu Software Center. When I open it, it closes automatically without any permissions. When I run it in a terminal I get this:

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__'

What's wrong? How can I fix it?