Haven't a clue, Andy
I can only suggest that you check that the silhouette files have the correct extension (.bmp). As long as they are in the same folder as the silhouettes that are showing, and you only have one instance of the software on your computer, there's nothing more that I can think of.
You could try downloading them again, (you need to restart RadarBox if you change silhouette files) and if that doesn't work, contact Support.