I have had this same exact issue before. I don't think it has anything to do with brb. In my case it didnt, and I thought the firmware update checked for brb around 40-50 % ? Try this, unplug the power cord and the battery on the motherboard and leave it unplugged for 30 minutes, then plug it back up and try to update it. If that doesn't work, and everything else you tried didn't work, then it is a problem with the flash to the NAND. The only way to fix that would be to reflash the console with a progskeet or other hardware flasher. I have a chechE01 right now that does the same thing. Only difference is, I can go to the XMb, but mine is on ofw 1.97 so there is no recovery mode to try that. I'm getting it reflashed so I will let you know how it goes. Please let me know if you get it sorted out and what worked for you. Good luck man.