Cannot install grub bootloader on windows 7 raid array

Package Ubuntu 12.04LS (64bit)

Co installing ubuntu 11.10 on windows 7 raid array worked.
Upgrade to 12.04 LS failed.
Clean install of 12.04 returned fatal error when trying to install grub bootloader.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.16
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 May 4 15:36:13 2012
InstallCmdLine: noprompt cdrom-detect/try-usb=true file=/cdrom/preseed/ubuntu.seed boot=casper persistent initrd=/casper/initrd.lz splash -- BOOT_IMAGE=/casper/vmlinuz
LiveMediaBuild: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
ProcEnviron:
 LANGUAGE=en_GB.UTF-8
 TERM=unknown
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)