Probably easier for me to just upload the missing image, actually. Just extract this and put the "img" folder into the "www" folder of your game, and if it asks, choose to merge folders.
Mega If you get the bug again with any other files, and you find they are missing, what you would do is just copy and paste a similar image (such as "D5-Green.png" in the battlebacks 1 folder), and rename the copied image. You can rename a file by just right clicking it and selecting "rename", and then you would just erase it and write in "D5-Blue.png", or whatever file was missing. You can then click "Retry" on the error screen, and it should end up working.