The SE7520BD2VD2 does not support 'Dual Rank' DDR2-400 Dimm's only 'Single Rank' DDR2-400 Dimms for full 16gb population. It is in the fine print foot note in the Server Manual, so I can see how one can easily miss that. You can tell Single Rank (Single Row Layout) from Dual Rank (Dual Row layout) by looking at the way the memory is laid out on each Dimm. I know it can be frustrating since you spent good money on more Dimm's than you can use. Just use the second set of 4x2gb Dimm's on another MotherBoard/Server if you have more than one. They might also come in handy if and when the other Dimm's fail.