How did you make the normal maps, that's the question. If you generated them from a height map in photoshop using the nvidia plugin, then the thing you should avoid is saving them directly from a height map to a dxt5_nm normal map. To quickly test this, you could try opening up your height map, saving it as a normal map but in regular dxt5 mode (if you're using the nvidia plugin), then opening up the blue normal map that generated in photoshop again and then resaving that in dxt5_nm mode with the options to generate normal map off (since it's already a normal map). Alternatively you could use crazybump to convert your height map to a blue normal map and then convert that to dxt5_nm. But that's just some ways, I have no idea how you created the normal for this. I do know that using the nvidia plugin to create the dxt5_nm normal directly from a height map creates problems.