Same problem occured with 5,5 - 80MB iPod
Divide by zero
at 00052E80
The archived build seems to work fine!
Lets see what happens now - this is my first try with RockBox.
Edit:
It took me a while to find out how to come back to original mode - while the error screen is on, Windows does not recognize the USB device, so you can't access the iPod!
This is how:
1. usual reset (Menu + Select Button for some seconds)
2. While screen is still black: Hold switch > on (This has to be done before the apple shows up!)
Edit: oops, just realized this is exactly what the manual says under 3.1.3 "Starting the original firmware" .. just that there was no "Loading original firmware" message in my case..
RockBox is exactly what I was looking for .. great!