Sounds like I have a similar issue with RAM not working in dual channel mode on the Asus P8Z77. I am using 2x8GB DDR3 sticks from a kit (CMZ16GX3M2A1600C10).
Either stick works fine in memory slot A1, but the M/B won't POST if I have both sticks in A1+B1 or A2+B2 (DRAM error light is on). I...