By the Gods I can hardly believe it... I deliberately left secure boot on for the install and to my utter amazement (exaggerating only a little) 14371 installed perfectly--as an upgrade install, no less--first time in many moons on my system...! Still, I did make my own ISO and upgraded in-place from that! (Lately the "flight" upgrade code coming through WU hasn't worked well for me--I suspect some kind of file corruption may be taking place through the upgrade/migration process.) But the ISO code seems to be working great, atm. My target system for Win10 Insider builds has about ~300 some applications and games installed over a few terabytes spanning several physical platter drives and SSD's--so doing a clean install every build is not my cup of tea, for obvious reasons!