How to flash a second image as multiboot

[twol]

Hi,
Number is no.
HDD is external and power is not have its own power suply. It is by the box

I think the issue is with the HDD having no power supply, ofgwrite msgs indicate (I believe ) that it cannot access the directory containing the unzipped image... but I really need to see the debug log.
When you flash an image there are a large number of read/writes and you really need separate power to the HDD.... this is true whether you use multiboot or just flash the basic image.
Having multiple images is great if you want to find the best image for yourself or you are into testing, otherwise if you happy with an image stay with it.