I have forgotten how it is in generation 5. But maybe you check your preferences wether the auto material refresh thingie is switched off by any reason.

But a complete black preview could be an indication as well that something is defined wrongly in the material - for example that you selected image mapping but have not defined an image there. Or moved a slider to zero that should not be there.

What you can do is to load a material that comes with Vue (even the default material the ground plane has is ok) and save this as it is. And see what is happening. Then you know wether it has to do with a setting in the material editor or not.

One day your ship comes in - but you're at the airport.