you may have installed a new kernel, without installing the boot-img. if you just want to get rid of multiboot : 1)download the fiasco image 2)extract the fiasco image into by flasher-3.5 -u /path/to/image 3)connect your n900 to pc into flashing mode. (connect cable to pc, press and hold "u" on n900 keyboard, connect cable to pc) 4)cd to where you extracted the fiasco image, and execute the command that you have quoted. your n900 should turn on and maemo start with default kernel (unless you deleted the default modules of course !!), remove multiboot and you are done !