I've observed this issue with two of your files only, "Background.png" as well as "yellow_right.png".
The file you believe is called "Background.png" is actually called "[some_invisible_character]Background.png".
This is from a directory property dump. The first entry is a file actually
The second entry is your file, the gibberish at the start of the file name represents the invisible character.
The solution is to simply rename the flle properly in Finder.
The problem with "yellow_right.png" is the reverse of the above. There the file is actually called "yellow_right.png", but in the script's <item> element, you had it called
/ 2 = "[some_invisible_character]yellow_right.png"
The solution there is to simply delete that entry from the item element and re-type it properly.