I think you might have a wrong version or done something strange to the new build for that to happen. Just add a png image with the beach_cave name to the www/img/faces folder.
This problem was also encountered in version 0.9.1 I searched for an image about beach_cave, but I didn't find it in all the folders.
You can fix it by adding a random png image named beach_cave
Happened to me too, weirdly. Wondered what caused it.
