He 111,
Have a look at this post.
http://forum.1cpublishing.eu/showthread.php?t=26236
If you have updated the Nvidia drivers you will have to re import your saved profile. What you will need to do is this: -
(1) install Nvidia inspector (if you have it installed already miss this step)
(2) Install "Luthiers" Sli code (you can find it in my first post with instructions on how to do this)
(3) It should then show as "Il2 Cliffs of Dover" in the Nvidia inspector profile list.
(4) Then export the profile list to some where like "My Documents". This will give you a copy to import back into Nvidia inspector when you have an update of drivers. (As there is no official support from Nvidia for Cliffs of Dover in their Sli profiles you will need to do this every time you have a driver update)
Hope this helps.