Dell xps 8900 RAM problems

Okay, so I have an XPS 8900, I have 32gb ram for it. I have tested all RAM and they work. Now my problem is I can only get it to boot with 16gb ram set next to each other, as soon as I try to put it in dual RAID it doesn't load. I tested each slot with one 8gb ram and they all work. What is causing this thing to not boot with all 32gb ram  or 16gb ram in dual raid? Yes all the RAM is the same.