I printed out a copy of the tutorial for installing BackTrack to a USB drive with full disk encryption, and followed along carefully as I tried it out. I've repeated the steps up to the install part several times, but the installation fails in the same way each time, telling me that I can't unmount the root partition. For some reason, when I start the installer, the dialog window where you choose the 'manual' partitioning always shows the sda instead of sdb drive (the USB drive). In the demo pictures, it's pointing to the sdb drive. I know the values aren't always going to be the same, but in this case they are.

I repeated this several times just in case I had missed something. I set the logical volume as the '/' dir with ext3 file type. This resolves to sdb5 on the USB drive. I set the sdb1 to '/boot' with ext3 file type. This resolves to sdb1. However, when I continue to the next dialog box, the summary says that changes are going to be made to partitions sda and sdb. It keeps trying to assign a swap partition to sda5. The demo images showed only changes pending to sdb. If I continue at this point, I get the error stating that '/' cannot be unmounted. Since it's supposed to install on sdb5 and is trying to write to sda5, I thought I'd made a mistake somewhere. I was unable to find any errors. But...

I thought somehow I might have accidentally mapped the sdb5 volume to a partition on sda, but that couldn't be. The 'fdisk' command encompasses all of the changes until finished inputting commands so I couldn't have done much wrong there, and when I looked at the partitions in the installer, it was clear that '/dev/mapper/vg-root' mapped to /dev/sdb5 due to their size values.

I tried doing the install off of a live disc, and also from an installed Backtrack on my laptop. Any thoughts on what could be causing this behavior would be very much appreciated.