lardman, the update will attempt to flash-and-reboot automatically, so that is likely the problem. If you're using an N810, you'll have to re-flash the old (chinook) kernel. You can do this without losing your current install and settings, but you need the linux-based (or OSX-based?) flasher program and an image of the old kernel (which you can extract using flasher from the chinook fiasco image).