grub-install on precise failed writing to a partition

When trying to install Ubuntu from today's daily-live, i chose to install GrUB to a partition, instead of the MBR. It failed, asked to try another partition, that also failed. Then apport came out.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.5
ProcVersionSignature: Ubuntu 3.2.0-21.34-generic 3.2.13
Uname: Linux 3.2.0-21-generic x86_64
ApportVersion: 2.0-0ubuntu3
Architecture: amd64
CasperVersion: 1.314
Date: Tue Apr 3 21:33:34 2012
InstallCmdLine: noprompt cdrom-detect/try-usb=true file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash -- maybe-ubiquity
LiveMediaBuild: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120403)
ProcEnviron:
 LANGUAGE=es_MX.UTF-8
 TERM=unknown
 PATH=(custom, no user)
 LANG=es_MX.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)