Does your texture for the body mat contain any more additional "." (dots) on top of the extension.
Could you post a couple screenshots of the material and textures from the material editor and the folder in asset manager? This will let us see what your seeing
A video of the process is always the best for us as it allows us to reproduce the issue at hand a lot easier.
We will help you the best we can
Thanks
p.s. You could always pm me the mesh and textures and i could try preparing it for you and see what causes the error.
The base unconverted mesh, textures etc.. will be required to test with.