I am trying to install BackTrack4 on an external USB Hard drive. It is the only drive connected. I have followed the manual installation instructions from the
offensive-security walk through, and everything went smoothly. No hang ups at all, but when i reboot and remove the live disk, i keep getting this error:

Kernel Panic - Not syncing vfs: unable to mount root fs on unknown-block(8,3)

What would cause this?