Puppy Unleashed on thumb drive: boot hangs at "switch root"

[polygonal]

I seem to have no luck in trying Puppy Unleashed (and any modification of pup_300.sfs); when my computer boots, it stops at "switch-root" and never goes past that. The computer boots fine if I use the normal version of puppy. I'm booting from usb, and after createpuppy script done its work, I simply copied pup_300.sfs, initrd.gz, and vmlinuz to my usb drive. I did omit some packages from my puppy unleashed package collection, but I don't think I removed anything essential (hopefully).

Can any one give me a pointer as to what might have gone wrong?

Many Thanks.