I think I may have got close to the cause. Poser 4 files were working fine, but not some Poser 5. So I did a comparison. Poser 4 doesn't use the Shader Tree system. Poser 5 does. And in Poser 5 a texture map is refeered to in at least two places, once in the section compatible with Poser 4, and once in the shader tree for that material. And there seems to be a difference in how the path/filename combination is stored. I strongly suspect the problem is in the Shader Tree, possibly in how Poser handles the path data for the file, but there may be other details I haven't found yet. And it's after midnight... Somebody else can worry about it now.