It is either a bad stick of memory, check it with memtest86, or it is the fact that the timings are too tight in which you could be getting a tRAS violation error.
Try both out and let me know what is happening. It could be something else but those are the first two off the top of my head.
<A HREF="http://www.stompfest.com" target="_new">Stompfest Sept. 13-14 - Indy. IN</A> - Should be some good gaming!!!