How to install images using boot-x ? help needed

I use dm800se . I can install merlin image using the menu "Install merlin image" which downloads files directlly from the feed, but I cannot use "Restore" to unpack the *.nfi files from the Bootx-backup directory. There is an error message "missing system files". I have installed nfidump v0.11 in my flash image. I cannot figure what are the "missing system files " ?