GA-EP45-UD3R and 2x2GB G.Skill PC-8500 DDR2-1066 dual-channel problem

Hey folks - I've done some searching and reading and found people with similar issues as me but no solutions yet.

I'm running an Intel E8400 Core2 on my new Gigabyte GA-EP45-UD3R motherboard with 2 sticks of 2GB G.Skill F2-8500CL5D-4GBPK memory.

The system will run stable with the memory clocked to its default 1066Mhz and installed in single-channel. It will also run stable clocked to 800Mhz and installed dual-channel. It will NOT however run stably locked to 1066Mhz and installed dual-channel. With the system doesn't get past the beep (no access to BIOS or anything until I remove a stick).

I have tried manually increasing the DRAM voltage to 2.1V to no avail.

Anyone have any other suggestions? Is it likely memory or mobo related?

I can provide more info if needed... Thanks so much; it's driving me crazy.