Atrocities, are you having a bad week or something? It's got to be the spicy food and Diet Coke binge you went on the other night.
Oleg is right one here. There is nothing wrong with your data files at all. It sounds as if you have a race that instead of using the Default_AI_Strategies.txt file has it's own particular racename_AI_Strategies.txt file, and the Fighter Attack strategy is missing from it. So when the default design creation file pulls that up it can't cross referance it and you get the error.
IIRC that Last time I got this error it didn't stop the game, it just comes up at the beginging of the turn.
Geoschmo