Sorry I didnt reply to your pm phoenix I was out of the country and had no internet access. The reason your textures were appearing white was because of the alpha channels. The original texture alpha controls transparency while the one in the normal texture controls specular lighting/gloss maps (the shiny metal bits) Saving the modified original as the normal gives you a messed up alpha. Your method of copying gets around this as would copying the alpha from the normal but if you're changing metal parts of the texture to cloth or vice versa you might want to modify the alpha as well

btw theres a couple of other ways to generate normal maps, the photoshop filter is the quickest but the results arent always great as can be seen on some of the game models