maybe the solution to your problem..
I had exactly the same problem with the boot disk , i was getting
Error: Could not stat device /dev/hda/ - No such file or directory.
the error is possibly an incompatibility in the system imager version.
when I was trying to create the boot disk from my image server I was getting a floppy disk timeout so I downloaded the floppy image from the link that the tutorial contains. I burned that image and I added the local.cfg file taking into account the unix line feeds, but it did not work.
Then I noticed that in the original tutorial falko was warning about the possible differences in versions of systemimager after 3.4. My version is 3.2.3-6 so i estimated that the downloaded image could be incompatible and tried the other way. in the image server i executed
mkautoinstalldiskette -config /var/lib/systemimager/my-client.local.cfg -out-file my-client-restore-disk.img
dd if=my-client-restore-disk.img of=/dev/fd0
after the floppy was ready and my image-server was running, the system was restored without problem.
I hope this works for you too.