un an attempt to triple boot my macbook, installer says that grub can't install to specified partition

[Dylan Meadows]

Attempting to triple boot my macbook.

On one hard drive:
-Mac OS X
-Windows 7
-Ubuntu

When installing Ubuntu, the installer says that grub cannot be installed on the partition, to please select another drive to install grub on.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubiquity 2.18.7
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CasperVersion: 1.340
Date: Tue Jun 10 21:59:16 2014
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper only-ubiquity quiet splash --
LiveMediaBuild: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)