Getting the same "No DEFAULT or UI configuration directive found!" in 2016-08-30 GENERIC image. Could you provide the CRC32 or MD5 of the images so that we could verify them?
I had the same problem with Generic 28 and 30 fresh install on my old atom, Generic 22 works but could not update because of not big enough system size.
I ran Gparted through ubuntu live cd and resized system partition a little bigger and the update works and no more boot problem.