Comment 2 for bug 1254447

Fortunately (for reporting the bug), after upgrading to 13.10, trying to upgrade to 14.04 has the same problem:

/home/mool 30 % sudo update-manager -d
[sudo] password for mool:
Checking for a new Ubuntu release
authenticate 'trusty.tar.gz' against 'trusty.tar.gz.gpg'
extracting 'trusty.tar.gz'
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-qwg0du/trusty", line 10, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-qwg0du/DistUpgrade/DistUpgradeMain.py", line 240, in main
    save_system_state(logdir)
  File "/tmp/ubuntu-release-upgrader-qwg0du/DistUpgrade/DistUpgradeMain.py", line 133, in save_system_state
    scrub_sources=True)
  File "/tmp/ubuntu-release-upgrader-qwg0du/DistUpgrade/apt_clone.py", line 149, in save_state
    self._write_state_sources_list(tar, scrub_sources)
  File "/tmp/ubuntu-release-upgrader-qwg0du/DistUpgrade/apt_clone.py", line 241, in _write_state_sources_list
    "./etc/apt/sources.list.d/"+source)
  File "/tmp/ubuntu-release-upgrader-qwg0du/DistUpgrade/apt_clone.py", line 246, in _add_file_to_tar_with_password_check
    for line in f.readlines():
  File "/usr/lib/python2.7/codecs.py", line 296, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf8' codec can't decode byte 0x9f in position 3: invalid start byte