Центр программного обеспечения Ubuntu не откроется

Когда я пытаюсь открыть Ubuntu Software center через терминал следующие шоу:

$ software-center
2015-03-03 13:07:01,990 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None'
2015-03-03 13:07:02,224 - softwarecenter.ui.gtk3.app - INFO - building local database
2015-03-03 13:07:02,225 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open()
Traceback (most recent call last):
  File "/usr/bin/software-center", line 130, in <module>
    app = SoftwareCenterAppGtk3(options, args)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 313, in __init__
    self._rebuild_and_reopen_local_db(pathname)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 532, in _rebuild_and_reopen_local_db
    rebuild_database(pathname, debian_sources, appstream_sources)
  File "/usr/share/software-center/softwarecenter/db/update.py", line 1148, in rebuild_database
    cache.open()
  File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 261, in open
    self._cache = apt.Cache(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 107, in __init__
    self.open(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 155, in open
    self._list.read_main_list()
SystemError: E:Type ‘WEW’ is not known on line 3 in source list /etc/apt/sources.list.d/mono-xamarin.list

Я не забываю вводить 'WEW' случайно, но я не уверен, как изменить это.