Two possiblities if that much of the RAM is showing up bad:
A: One of the sticks went bad, in which case you should get a replacement stick. Test all your sticks one at a time to weed out the bad ones.
B: Theres a lower-level config problem with the modules [voltage, timings, etc], causing one of the sticks to not function properly.
Test one stick at a time. If you still get errors, then the stick is likely bad.