So it's a superslim 12Gb?
If so you could always try putting a sata hdd in it, see if the installation succeeds on hdd.
With a 12Gb superslim running on emmc memory, chances are the issue isn't related to the storage space though. You should try anyway if you have a spare sata hdd handy, it will take a few minutes & you never know but if I had to guess I think I would lean in favour of either the hardware issue or the case of a CFW patch that should not have been applied, again assuming that the PUP is valid, the device partitioned correctly, the file path correct & in upper case, no USB hub, no fancy USB devices the simpler the better, etc..