install is crashed

[koban]

 when insall is continuing, it was crashed.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.29
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic-pae 3.2.14
Uname: Linux 3.2.0-24-generic-pae i686
NonfreeKernelModules: wl
ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
CasperVersion: 1.315
Date: Wed Apr 16 18:48:33 2014
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash -- debian-installer/language=ja keyboard-configuration/layoutcode?=jp keyboard-configuration/modelcode?=jp106 maybe-ubiquity
LiveMediaBuild: Ubuntu 12.04 "Precise" - Build i386 LIVE Binary 20120501-03:27
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 LANG=ja_JP.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[koban (letter-msa)]

 I'm so tired.

[Ubuntu Foundations Team Bug Bot (crichton)]

Exception during installation:
Apr 16 07:38:13 ubuntu plugininstall.py: Traceback (most recent call last):
Apr 16 07:38:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 1730, in <module>
Apr 16 07:38:13 ubuntu plugininstall.py: install.run()
Apr 16 07:38:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 55, in wrapper
Apr 16 07:38:13 ubuntu plugininstall.py: func(self)
Apr 16 07:38:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 174, in run
Apr 16 07:38:13 ubuntu plugininstall.py: self.install_language_packs()
Apr 16 07:38:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 664, in install_language_packs
Apr 16 07:38:13 ubuntu plugininstall.py: self.do_install(self.langpacks, langpacks=True)
Apr 16 07:38:13 ubuntu plugininstall.py: File "/usr/lib/ubiquity/ubiquity/install_misc.py", line 856, in do_install
Apr 16 07:38:13 ubuntu plugininstall.py: with Cache() as cache:
Apr 16 07:38:13 ubuntu plugininstall.py: AttributeError: __exit__
Apr 16 07:38:13 ubuntu plugininstall.py: