Lubuntu 12.04 ok on usb stick but failed install to PC

[cheapo]

As above. I have been running Lubuntu 12.04 for several days from a USB stick. But installing failed during a full HD install from the same downloaded live CD

Applet says extra debug info will be attached.

Have a nice day.
Pete.
:¬)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.29
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
ApportVersion: 2.0.1-0ubuntu5
Architecture: amd64
CasperVersion: 1.315
Date: Fri Apr 25 17:27:59 2014
InstallCmdLine: file=/cdrom/preseed/lubuntu.seed boot=casper only-ubiquity initrd=/casper/initrd.lz quiet splash --
LiveMediaBuild: Lubuntu 12.04 "Precise Pangolin" - Release amd64 (20120423)
ProcEnviron:
 LANGUAGE=en_GB.UTF-8
 TERM=unknown
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu Foundations Team Bug Bot (crichton)]

Exception during installation:
Apr 25 16:27:30 lubuntu plugininstall.py: Traceback (most recent call last):
Apr 25 16:27:30 lubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 1730, in <module>
Apr 25 16:27:30 lubuntu plugininstall.py: install.run()
Apr 25 16:27:30 lubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 55, in wrapper
Apr 25 16:27:30 lubuntu plugininstall.py: func(self)
Apr 25 16:27:30 lubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 174, in run
Apr 25 16:27:30 lubuntu plugininstall.py: self.install_language_packs()
Apr 25 16:27:30 lubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 664, in install_language_packs
Apr 25 16:27:30 lubuntu plugininstall.py: self.do_install(self.langpacks, langpacks=True)
Apr 25 16:27:30 lubuntu plugininstall.py: File "/usr/lib/ubiquity/ubiquity/install_misc.py", line 856, in do_install
Apr 25 16:27:30 lubuntu plugininstall.py: with Cache() as cache:
Apr 25 16:27:30 lubuntu plugininstall.py: AttributeError: __exit__
Apr 25 16:27:30 lubuntu plugininstall.py: