#1 — `TypeError: Odd-length string` while decoding username

Toni Müller reported the following:

In conjunction with Plone 4.0.7, I get this error once in a while:

2011-08-03T21:36:03 ERROR ZServer uncaptured python exception, closing channel <ZServer.HTTPServer.zhttp_channel connected 127.0.0.1:34242 at 0x89f76c8 channel#: 14537 requests:> (
<type 'exceptions.TypeError'>:Odd-length string
[/usr/lib/python2.6/asyncore.py|write|86]
[/usr/lib/python2.6/asyncore.py|handle_write_event|447]
[/usr/lib/python2.6/asynchat.py|handle_write|174] [/usr/lib/python2.6/asynchat.py|initiate_send|226]
[/mounts/7/zope/eggs/Zope2-2.12.18-py2.6-linux-x86_64.egg/ZServer/Producers.py|more|34]
[/mounts/7/zope/eggs/collective.usernamelogger-1.1-py2.6.egg/collective/usernamelogger/__init__.py|log|44]
[/mounts/7/zope/eggs/collective.usernamelogger-1.1-py2.6.egg/collective/usernamelogger/__init__.py|username|18]
[/mounts/7/zope/vplone4/lib/python2.6/encodings/hex_codec.py|hex_decode|42])

Then the affected Zope server restarts, and the user's session is being
terminated. He sees this on his screen: "502 - Bad Gateway", and then
calls support.

The environment is Debian Squeeze amd64 with

Python 2.6.6-3+squeeze6
Plone 4.0.7, installed using buildout
collective.usernamelogger 1.1