I got a message saying that the background to one of my Challenges was all white. The game plays fine, but if there is no background image, the game will display an all white background instead. I used a Tribe background, but don’t require the player to have the Tribe expansion to play (which he apparently doesn’t have). I had assumed the game bundled the background image with the challenges. Oops! Apparently not.
Cliff, Is it possible for the game to substitute a random existing background if the default isn’t found?