New X2 causing problems with memory?

I'm having issues in both dual channel and single channel memory modes after installing a Toldeo AMD X2 3800+, socket 939. This is a computer I built myself, previously housing a AMD 64 3200+. The motherboard is the Chaintech VNF4 with the latest BIOS (3/2006). The memory is Corsair ValueSelect C2.5 DDR400, not overclocked.

After dropping the X2 in, I am having severe issues with errors in the memory. Dual channel (slot 1, slot 2) worked fine with the AMD 64, but Vista does not boot with the X2 installed. When I place the modules in single channel (slot 1, slot 3), Vista boots but eventually crashes and restarts the computer. Only when I boot through a single RAM stick does it remain stable.

I ran error-checking on the drive several times, with no problems. I ran Memtest86+ on both sticks individually for an hour with no errors. When running the test in dual channel mode, it consistently freezes at 5:30 mark. When running the test in single channel mode, nearly 400 errors occur within the first few minutes.

Any ideas what is wrong? I have reset CMOS and ESCD several times. I'm thinking about reflashing the BIOS next.