I'm following Plailect's guide, currently at Part 4, section V, step 10. Lumia 5.5 and 6 don't work (they boot into black screen so I cannot do anything). I tried downgrading with Lumia 5.3.1 but I get the NFIRM error. Then I tried downgrading with Lumia 5.4 but I get the same NFIRM error. I'm desperate, how do I solve this?