fatal error grub failed to install on root partition

[wagung]

i wan to install ubuntu 11.10 Beta 1 dual boot with windows seven,
and i plan to install the grub2 to in root partition sda6 (btrfs filesystem)

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: ubiquity 2.7.25
ProcVersionSignature: Ubuntu 3.0.0-9.15-generic 3.0.3
Uname: Linux 3.0.0-9-generic i686
Architecture: i386
CasperVersion: 1.280
Date: Tue Sep 6 08:15:31 2011
LiveMediaBuild: Ubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu Foundations Team Bug Bot (crichton)]

Exception during installation:
Sep 6 08:15:13 ubuntu plugininstall.py: Traceback (most recent call last):
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 1667, in <module>
Sep 6 08:15:13 ubuntu plugininstall.py: install.run()
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 55, in wrapper
Sep 6 08:15:13 ubuntu plugininstall.py: func(self)
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 199, in run
Sep 6 08:15:13 ubuntu plugininstall.py: self.configure_bootloader()
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 944, in configure_bootloader
Sep 6 08:15:13 ubuntu plugininstall.py: old_bootdev = self.db.get('grub-installer/bootdev')
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/lib/python2.7/dist-packages/debconf.py", line 60, in <lambda>
Sep 6 08:15:13 ubuntu plugininstall.py: lambda *args, **kw: self.command(command, *args, **kw))
Sep 6 08:15:13 ubuntu plugininstall.py: File "/usr/lib/python2.7/dist-packages/debconf.py", line 81, in command
Sep 6 08:15:13 ubuntu plugininstall.py: status = int(status)
Sep 6 08:15:13 ubuntu plugininstall.py: ValueError: invalid literal for int() with base 10: ''
Sep 6 08:15:13 ubuntu plugininstall.py:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Gary M (garym)]

Extract from attached UbiquitySyslog :

Sep 6 08:04:49 ubuntu grub-installer: info: Installing grub on '/dev/sda6'
Sep 6 08:04:49 ubuntu grub-installer: info: grub-install supports --no-floppy
Sep 6 08:04:49 ubuntu grub-installer: info: Running chroot /target grub-install --no-floppy --force "/dev/sda6"
Sep 6 08:04:51 ubuntu grub-installer: /usr/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea..
Sep 6 08:04:51 ubuntu grub-installer: /usr/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged..
Sep 6 08:04:56 ubuntu grub-installer: /usr/sbin/grub-setup: error: cannot read `/@/boot/grub/core.img' correctly.
Sep 6 08:04:56 ubuntu grub-installer: error: Running 'grub-install --no-floppy --force "/dev/sda6"' failed.