Ram stick both work individually, but not together.

Machine came with 2 x 8GB Ram, I decided to upgrade and ordered 2 x 16GB Timetec from Amazon. I installed them, booted fine, then shortly after hard crashed and got this screen:

Rebooted many times and it kept happening at random times with no warning. Ran Windows Memory diagnostic and there were no errors. Swapped the modules around and made sure they were properly seated, no difference. 

Decided to try individual modules and everything works fine. Each module in Slot A works fine, each module in slot B works fine. Put them back together, crash. I'm a bit stumped.