That error message you get shrub77 indicates that you have v1.4 of the game, and you need v1.5 for the Dark Waters mod to function correctly. Version 1.5 of the game has the U-Boat Missions Add-On. I cannot find that anywhere currently. If you are in the US though, the Ubisoft Store has
Silent Hunter 4 Gold Edition for $3.40US, which is a really good deal. That is the full v1.5 of the game with the UBoats in it...
