My thought is one of the sticks is in the process of 'dying' becoming bad. I would re-seat the RAM and make sure the DIMM slots aren't loaded up with dust; use compressed air to clean before removing RAM and then re-clean the DIMM slots. Examine the RAM's contacts for discoloration.
If the problem persists then contact OCZ for a replacement. Keep in mind OCZ no longer produces RAM so they may need to change out the entire kit for something else.
Run Memtest for 4-passes using one of the bootable (ISO) options, and failures report to OCZ and request an RMA. Memtest -
http://www.memtest.org/#downiso