Cool Unable To Update Cm 4.1.2 Assertion Errors

I'm trying to go from 4.1.2 to the next stable CM Rom.
My first attempt I received assertion errors. did some research on this and find it very confusing ie…. bootloader updates , remove assertion line in the installer script. I even went to CM and tried to use there updater and almost bricked my phone.

I have read the post by CM regarding the firmware change but haven't seen the fix yet or at least read somthing I trust on my own.

My Recovery is TWRP v2.6.3.1

Model # SGH-T999
Android Version 4.1.2

Baseband Version T999ULLJ4

Kernel Version: 3.0.48-cyanogenmod-ge67063c blinky-ghost@cyanogenmod #2 Tue Nov 13 23:04:58 PST 2012.

CPU ARM7 Processor rec0(7l)

Cyanogen Version 10-20121114-NIGHTLY-dt2tmo

Build Date: Tues Nov 13 23:02:54 PST 2012
Build Number: cm_d2tmo-userbug4.1.2JZO54K eng.20121113.230148.test-keys

Can someone point me in the right direction?
Thanks in advance..