Cannot install any custom ROM

Hi,
I've got a SM-T531 tablet and I hate the official ROMs. They're bloated and ugly. I searched around and found 2 custom ROMs which I would love to try out. I have flashed ROMs on my previous devices but never had any issues. Here's what I have done:

First I have flashed CF-Autoroot using Odin and it was successful. I could install apps with root permission, it was all good.
Then I wanted to install a custom ROM. I followed the instructions in this link:
http://forum.xda-developers.com/tab-...p-3-1-t3084757

I downloaded the latest TWRP:
https://www.androidfilehost.com/?w=files&flid=40746

The ROM:
https://www.androidfilehost.com/?w=files&flid=40978

GApps (I downloaded the SOKP-Mini-Gapps.L5.1.1-R-1.0-20150801.zip file):
http://downloads.sonic-developers.com/gapps/

Then used ODIN to flash the TWRP file, it was successful. Next I used the "Home+Volume Up+Power" to go to the recovery mode. After that I cleaned (Factory Reset) and used the "Install ZIP" to flash the ROM and then GApps. All finished without any issues.

But when I reboot I get the following error (same colors):

Quote:

kernel is not seandroid enforcing set warranty bit : kernel

It stops there and never goes to any boot screen. Just freezes.

It's the same with the ROM mentioned in the following link:
http://forum.xda-developers.com/tab-...a-0-7-t2963906

Note: When I flashed the stock firmware, the tablet boots perfectly fine. But when I try to install custom ROMs I get this.
I have never seen this error before. What am I doing wrong?

I would appreciate any kind of help. Thanks in advance.