dual channel problems. limits fsb?

I have had the same limit on my fsb with three seperate boards and two cpus. My current setup is in my sig. When I use just one stick of memory 200fsb is stable on 3dmark03, and memtest. Either stick passes. When I run dual channel I get errors on test 5 in memtest and lockup on 3dmark03. I have tried various settingd currently @ 11,3,3,2. The memory is corsair xms 3500c2 2@256. Any suggestions??

Which dimm slots are you using for Dual Channel?

This board has 4 slots. I'm using the 1st of each controller. SO 1st, and third. Bios on boot shows dual channel. when I tried each by it's self yhe bios did not report dual channel.