Looking at this link you will find tested third party memory modules for your motherboard. From the list you can use 4 sticks of the 4gb modules. There is nothing about 8 gb modules listed. So this can mean that they are not compatible?
You can try updating the bios and see if the problem dissappears.
Actually, I am not using any 8GB sticks. I was using four 4GB sticks, I just bought 2 dual channel kits to get there instead of buying 4 individual 4GB sticks. I have 4 identical sticks of of 4GB RAM, it's just that I can only use 1 or 2 4GB sticks at a time and not all 4.
Thanks for looking though!