external usb drive probs

[n00rt]

hi - i have installed hardy onto an old usb drive i had knocking around - i did a guided install - use full disc on the drive and the installation went smoothly when i reboot and choose the drive to boot from grub loads and gives me the option of operating system to boot into - ubuntu - safe mode, memtest etc but choosing any of those gives me the error 17 cannot mount this partition.

.. is there any way around this - i have found several related error 17 threads but none that resemble mine.

thanks in advance..