Quoting Rob Klingsten <bladex@coldstripe.com>:
Yes, I have the DIMMs in banks 1 and 2 out of 4 and I've removed and reseated them; I have swapped out the SATA cable, there are no PCI or PCI Express cards (system is headless.) And it looks like it was just that easy; I pulled one DIMM and ran the system on a single 512, problem gone; I wrote out 3 separate 100gb files without incident. It makes no sense to me as the RAM was fine in the other system, I never had problems.
Sometimes dimms just need to be re-seated. Have you tried to put the stick back in and confirm that your problems come back?