booted from USB, started raid array, attempted to install 13.04 desktop on md0. Grub install fails on all drives, install aborted

[Rob Andrews Consulting]

root@ubuntu:/home/ubuntu# mdadm --detail /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Thu Aug 1 13:18:52 2013
     Raid Level : raid1
     Array Size : 234298176 (223.44 GiB 239.92 GB)
  Used Dev Size : 234298176 (223.44 GiB 239.92 GB)
   Raid Devices : 3
  Total Devices : 3
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Thu Aug 1 16:18:20 2013
          State : active, degraded, recovering
 Active Devices : 1
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 2

 Rebuild Status : 16% complete

           Name : ubuntu:0 (local to host ubuntu)
           UUID : bbe2d60a:79577e97:a8b6471e:674da82b
         Events : 3522

    Number Major Minor RaidDevice State
       0 8 1 0 active sync /dev/sda1
       1 8 17 1 writemostly spare rebuilding /dev/sdb1
       2 0 0 2 removed

       2 8 33 - writemostly spare /dev/sdc1

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: ubiquity 2.14.6
ProcVersionSignature: Ubuntu 3.8.0-19.29-generic 3.8.8
Uname: Linux 3.8.0-19-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
CasperVersion: 1.331
Date: Thu Aug 1 16:15:10 2013
InstallCmdLine: initrd=/ubninit file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash -- BOOT_IMAGE=/ubnkern
LiveMediaBuild: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)