Nope, not a texture problem. Its poser trying to smooth across the surfaces. Basically poser smooths everything and ignores smooth groups. Its taking the normals at the edge of the lips and averaging it with skin polygons at the top of the lip. What you're seeing is some shading artifact. I'm assuming that's some kind of puffy lip MT. Since the MT is changine the angle of the lips vs the skin, you'll get some odd shade effects. Its kind of the same reason the nostrils are glowing. One thing you can try is to make sure the hilight and color of the lips match as much as possible to the face skin colors. That should help some.