Material as Picture/texture


I am using Rhinos 6 on Windows.

I add a material to a surface with picture/texture and then selected a .png.
The material shows correctly on the windows explorer preview and also when I render.
But when I open the file the material doesn’t show at all. I can then exchange the .png and it works correctly. But after saving the file there is the same problem again.

Any suggestions on where the problem could be?

Thanks Roland

post a file and materials?