You don't have your equipment prefixed correctly.
ARMOR_PREFIX = "Equipment/a"
That slash means that Equipment is a folder, and its looking in that folder for a file names "a17.png", not "Equipmenta17.png"
Either rename your files with a simple "a" and "w" then the number, and place them in a new folder in the Characters folder named "Equipment", or you can simply take the "/" out of the prefix configuration.