Please use instead this mod which works without expansion as a bonus
https://github.com/salutesh/Community-Loading-Screen
For more informations about this sample please follow:
https://github.com/salutesh/DayZ-Expansion-Scripts/wiki/%5BModding%5D-Adding-custom-loading-screen
Near the end of this page you should have a quick tutorial: https://github.com/salutesh/DayZ-Expansion-Scripts/wiki/%5BModding%5D-Adding-custom-loading-screen
The path of your pictures is incorrect or the naming is wrong. The mod was not able to find the picture(s).
It could also be because your DayZ Tools "Addon Builder" doesn't include json files.
The path to your scripts is incorrect or it failed to compile the pbo containing the scripts.