Very often after I close Blender, then restart and load a .blend with some textured meshes, the image maps won’t “refresh” upon loading. I’ll see just a magenta shade over entire things.
In Adobe InDesign or similar, there are “linked” files and “included” files. If something is included, it’s part of the source file and it doesn’t matter where the original image is. If something is “linked”, and if you move the original image file, InDesign gives you a crappy low-res proxy and obviously you can’t go to press with whatever you’re working on.
I figure that Blender is doing something similar.
So, I can go in and “re-open” the image file with no problem. I usually don’t even move them. I just want to figure out what I have to do so that I don’t have to tell Blender each time.