I downloaded sponza_obj.rar (sponza.obj + sponza.mtl) and sponza_textures.rar from the Crytek site. It looks like that there is lack of gi_flag.tga. Where I can find the missing texture ? Moreover the texture pack contains many specular texutres but .mtl file doesn't have paths for them. Why ? Next the brick material has following record:
map_bump textures\spnza_bricks_a_diff.tga It make no sense.
A valid Crytek Sponza package is available here: http://casual-effects.com/data/index.html All required textures are in-place.