One note ...

On the normal map, it appears as though it is inverted such that the areas that should be raised are lowered. Take a look at the nostril, for example. It is raised instead of lowered. Same with the indentations on the lips, and the eyebrows.

I am not familiar with GIMP, but what you would do in Photoshop is open up the normal map in Photoshop, and then go into the "Channels" palette. Then you invert ONLY the GREEN channel, which will "flip" the directions of what is up and what is down. (As Caisson mentioned, there are two formats that differ in what is raised and what is lowered ... Poser prefers Open GL, and many normal map utilities seem to default to DirectX which is probably preferred by game engines)

Otherwise, check whatever utility you used to create your normal map, and check to see if there is an INVERT NORMAL MAP feature there.