Assign wallpaper to existing skin

I use WindowBlinds 5 and it's a great product. I quickly found an existing skin that I liked (Aura) except for the wallpaper. I changed the wallpaper under "Properties" in Windows XP and everything works well. When I restart or turn on the computer after a shutdown, however, WindowBlinds reverts back to the original wallpaper associated with the skin. How do I get my chosen wallpaper to be the default? Thanks!