Memory errors could be side-effect of wrong timings. Before you RMA the sticks:
Make sure that BIOS DRAM settings are set on "auto".
If it already is, then set it on "manual" and use this formula
CAS# latency (Tcl) - this value should be known to you
Min RAS# active time (Tras) - this value should be known to you
RAS# to CAS# delay (Trcd) - this value should be known to you
Row precharge Time (Trp) - this value should be known to you
Row cycle time (Trc) = Tras + Trp
Row refresh cyc time (Trfc) = Trc + 4
P.S. You can use
CPU-Z to check your current memory timings and SPD timings table.
I had to use this formula on my DDR memory. I'm not sure whether this works on DDR2 memory.
Unsolved 
