Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 858, in add_key_clicked
    if not self.backend.AddKey(chooser.get_filename()):
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
DBusException: org.freedesktop.DBus.Python.UnicodeEncodeError: Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/lib/python2.7/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 279, in AddKey
    return self.add_key(path)
  File "/usr/lib/python2.7/dist-packages/softwareproperties/SoftwareProperties.py", line 720, in add_key
    if not os.path.exists(path):
  File "/usr/lib/python2.7/genericpath.py", line 18, in exists
    os.stat(path)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 18-24: ordinal not in range(128)