here grml-debootstrap confuses the configuration of the running system with the 
target.
it only produces a bootable system if the target system is compatibel with the 
source system.

running system:
   /dev/hda (something else)
   /dev/hdb (grml-debootstrap on)
target system:
   /dev/hda (root, installed from the running system where it is /dev/hdb)

grml-debootstrap --target /dev/hdb1 --grub /dev/hda --groot hd0,0 ...
the problem is, that /dev/hdb1 got the root device in the target system which 
should be hda1.