Comment 1 for bug 8136

I think this is quite different from bug #7256, judging from the symptoms you report.

I bet that the first stage bootloader as written to the bootstrap partition has
the wrong path to the second stage bootloader wired into it. From the installer,
could you please:

  * run through the UI up to partitioning (don't finish partitioning, though)
  * change to the second virtual console (Command-F2, Command-Fn-F2, or similar)
  * mkdir /target
  * mount /dev/discs/disc1/part<your Ubuntu root partition number> /target
  * chroot /target
  * mount -t proc proc /proc; mount -t sysfs sysfs /sys
  * ofpath /dev/hdb<your bootstrap partition number>
  * umount /proc; umount /sys
  * exit
  * umount /target

I'd also like to know what kind of disk hardware you've got.