When I start my game I get this error message:

Info: Fullscreen: no
Info: Language: en
Info: Lua console: yes
Info: Turbo mode: no
Info: Simulation started
Fatal: Data file 'sprites/' is a directory

What is causing this?

(My game is rather small. 2 rooms and one self-made item.)

[Spikira]

Too lazy to explain myself, so here you go:
https://forum.solarus-games.org/en/index.php/topic,1289.msg7654.html