Upgrade to quantal won't start

[Bas van den Dikkenberg]

I just run the do-release-upgrade like following:

root@ns3:/etc# do-release-upgrade
proxy '\' looks invalid
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]
Get:2 Upgrade tool [1198 kB]
Fetched 1198 kB in 0s (0 B/s)
authenticate 'quantal.tar.gz' against 'quantal.tar.gz.gpg'
extracting 'quantal.tar.gz'

Reading cache

Checking package manager

Continue running under SSH?

This session appears to be running under ssh. It is not recommended
to perform a upgrade over ssh currently because in case of failure it
is harder to recover.

If you continue, an additional ssh daemon will be started at port
'1022'.
Do you want to continue?

Continue [yN] y

A fatal error occurred

Please report this as a bug and include the files
/var/log/dist-upgrade/main.log and /var/log/dist-upgrade/apt.log in
your report. The upgrade has aborted.
Your original sources.list was saved in
/etc/apt/sources.list.distUpgrade.

Traceback (most recent call last):

File "/tmp/update-manager-04gFJk/quantal", line 10, in <module>
sys.exit(main())

File "/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeMain.py",
line 240, in main
if app.run():

File
"/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeController.py",
line 1764, in run
return self.fullUpgrade()

File
"/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeController.py",
line 1616, in fullUpgrade
if not self.prepare():

File
"/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeController.py",
line 429, in prepare
self._sshMagic()

File
"/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeController.py",
line 299, in _sshMagic
"Do you want to continue?") % port)

File "/tmp/update-manager-04gFJk/DistUpgrade/DistUpgradeViewText.py",
line 216, in askYesNoQuestion
res = sys.stdin.readline().decode(ENCODING, "backslashreplace")

TypeError: decode() argument 1 must be string, not None
=== Command detached from window (Thu May 9 13:34:06 2013) ===
=== Command terminated with exit status 1 (Thu May 9 13:34:06 2013) ===

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager (not installed)
ProcVersionSignature: Ubuntu 3.2.0-41.66-generic 3.2.42
Uname: Linux 3.2.0-41-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.2
Architecture: amd64
Date: Thu May 9 13:44:09 2013
InstallationMedia: Ubuntu-Server 12.04 LTS "Precise Pangolin" - Release amd64 (20120424.1)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=C
 SHELL=/bin/bash
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2013-05-09 (0 days ago)