TWIN2X4096-6400C5C will not post with both

I've got an Asrock N68C-GS FX motherboard running an AMD Athlon 64 x2 processor. I picked up a TWIN2X4096-6400C5C G because it was on the approved memory list from ASRock. When I put both sticks of memory in, it will not post. System will power up but nothing else. If I just run on stick of memory, does not matter which one I have tried both, then it will post. Are there any bios config settings I should try? I have already tried manually setting the frequency to 400/800 and inputting timings of 5-5-5-18 which is written on the sticker on the memory. Tried at 1.795v and 2.065v with no difference either, just refuses to post with both. Any ideas?