You should have a total of 16 maps/images. Each has to be exactly 512 pixels by 512 pixels. If they are even a pixel smaller, I have seen lines similar to what you're seeing. I know how frustrating it can be!
I've also seen the lines when I've had "wet edges" turned on (I used Photoshop when I used to Mod). It makes the outside edge of each image a light color, similar to what you're seeing.
Could either of these be happening with your images?
Of course there are other possibilities, depending on the steps taken to create the mod, but the 2 things I mentioned are a good start.