I'm not an expert (as I'm sure you can tell from my own thread about Visitor-related issues) but I think you need to open the file as a "Color Texture Image (*.bmp;*.jpg;*.png)" in Wilbur. If memory serves, I encountered the same issue and ended up resolving it that way. That said, I'm getting Visitor crashes later in the tutorial so you may want to confirm with someone who's created an island successfully.
Hope this helps!