What other modules do you have in there and are they double-sided as well? Your motherboard supports only so many banks and with double sided modules, those are 2 banks. If your other modules are double-sided as well, you may be hitting that limit.
[Edit] Well, nevermind. The 810 chipset supports 4 banks of memory so 2 double-sided modules should work. Don't know what the deal is with yours.
Unless - how many chips are on each side of the module? If there are only a few, it may still be high-density but instead of putting all of the chips on one side like they normally do, they just split them up between both sides.