Its single rank, so that shouldn't be an issue.
Go to bios and change CR to 2T (from 1).
See if that helps.
Try the next lower clock to see if you can lower voktage a bit.
Use memtest86+ (not just memtest, thats different), burn to cd and boot from it.
Run 2 full test and see if it finishes without errors.
Then run test 5/6/7 a few times each, those are more sensitive to oc..