i have one VGA and one DVI connector on my graphics card, my monitor is an SXGA monitor, i thought i would try using the DVi-Analouge connector with my monitor, and when i try to use it, my TFT monitor wont actually display a picture, i have to plug it straight into the VGA port, My TFT uses a VGA connector like most CRT's use., my old DELL 15" CRT works ok with the DVI-Analouge connector. you may be wondering why i am asking this as i have an analouge connector on my graphics card, its so i can be sure if or if not my monitor will work with any of the more modern graphics cards with dual DVI.
My best guess is that adapters are often-times finicky and may work with one monitor and not the other.
Not sure, but you might check your manual regarding any particular setup for analog LCD's. You may only be able to use it on one port but not the other.