There was some change (from A6 to A7) in how gamestudio engine handle tga if i'm not mistaken? I have no access to sphere2 atm, but maybe the tga's that came with sphere2 must be update in psp or another tool. That or the sphere2 script needs adjustment.

Sorry for the late reply, but since the updates of GameStudio take so long i've started working with other tools for now.