Try the following:
1. Get into your BIOS and set the RAM specs manually, and then increase the voltage by ~.1v. Be warned though, Intel states that you can damage your CPU by raising your DRAM voltage higher than 1.65v. To that effect, there have been people on this forum who've gone higher than 1.65v and not run into problems.
2. If you don't want to raise your DRAM voltage, you may want to consider loosening the timings.
3. If your CPU is overclocked, you may have to lower the DRAM frequency.
4. Run
MemTest86+ on the two troublesome sticks, but with only one installed at a time.