In trouble time this site helped me a lot rather that fcking XDA!
Xperia Z 10.3.1.A.2.67 firmware Update Rolled Out - Minor Bug fixing | Xperia Guide
The build they have used in both the [STOCK ROM] installation thread are corrupted. I've tried to update my phone numerous times by following XDA process but it just bricked my phone each time.
Then, after two days of battle I won with the help of the previously mentioned site's help.
My phone: Xperia Z with .244 build rooted
Task I wanted to achieve: Install .67 and then root it.
Why I fcuked up: Like all precious updation method, I went installed the new .67 ROM from recovery but the installation threw error in halfway. The Kernel refused to be flashed from flashtool.
I then (without taking the backup of Titanium backup's backup) installed an older ROM i.e. .434. Rooted it and installed recovery and installed .67 ROM from recovery. This time the ROM was received from another source who claimed they have this full-proof method.
Bricked again.
Then I thought may be the diff. between two ROM in version is too much, there could be some issues in directory structure issue. So I installed .434, then .244 and then .67. Failed installation. Bricked again.
Then this website helped me from my misery.
I trusted XDA too much I guess. There are reasons behind me having trust issues!