You may need to connect one as the master and the other as the slave.. Refer to the pin configurations at the back of the drives near the place where you connect the power and the IDE cables.. Between the two junctions, you'll see the config pins..http://i.t.com.com/i/tr/gallery/ee/addstorage/IMG_7594.JPG
Refer to the settings regarding those pins (generally given at the top of the drive).. Connect on drive as master and the other as slave.. It just might work..