I just wanted to share my experience for v1.5.x and my WNDR3700 v1.
The router is booting until v1.5.6, then with v1.5.7 -> 1.5.11 no chance to have a successful flash !
Does anybody have the same pb ?
Finally I successfully flashed v1.5.11, beginning from v1.5.7 first.
The boot was ok with green led instead of orange ones like last time. I had to deactivate my network card (Atheros AR8131) and reactivate it in order to access the router.
I was not able to keep my settings otherwise I lost some menus (the new ones like plugins). But the new features are great, I love this firmware
I have WNDR 3700 v2
i have similar issue ... but i think it is caused by windows 7,8,8.1 ... when i use vmware with windows XP than flash is succesfull