installer crashed - can't install boot loader to usb hard drive

[Rusty2013]

install looks normal until time to configure bootloader (grub?). installing xubuntu 11.10 from bootable cd to 320G samsung external usb hard drive in system without internal hard drive. tried on two different computers with what used to be a working usb hard drive running xubuntu 10.04 xfce installed the same way. gives an option to install bootloader to another location, which there aren't any, or to complete installation noting that a bootloader will have to be installed manually (the only choice) then fails.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: ubiquity 2.8.7 [modified: usr/lib/ubiquity/ubiquity/misc.py]
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic i686
ApportVersion: 1.23-0ubuntu3
Architecture: i386
Date: Thu Feb 9 02:24:37 2012
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Reviewing your log files attached to this bug report it seems that there is a problem with the disk to which you are trying to install Ubuntu. I'd recommend performing a back up of your existing operating system and then investigating the situation. Measures you might take include checking cable connections for your disks and using software tools to investigate the health of your hardware. In the event that is is not in fact an error with your hardware please set the bug's status back to New. Thanks and good luck!

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]