Cannot Upgrade OTA Firmware (Currently 6.5.35)

My phone gor bricked and I had to unbrick it using this method http://www.asus-zenfone.com/2014/11/...-4-a400cg.html
So I was able to boot my phone and installed 6.5.35.
Now I want to upgrade using OTA firmware (WW-6.6.3) but when I do, it always restarts and goes to droidboot window and the upgrade fails.
Any help from you guys?