Is there any way I can share my whole data folder?
You could use something like gitlab or GitHub, they're designed for sharing exactly that kind of thing.
I don't know what might be causing that error- but maybe think about that you recently did before you got it.
The other day, for example, I was trying to call "hero:start_attack()", before the hero had the attack ability. The error I got was "Error: Cannot find sound file 'sounds/.ogg'
So it might be like, your code is looking for
"sprites/"..[a variable]
but the variable is nil or equal to "", so it's trying to just use "sprites/" as a sprite, when in fact it's a directory.
Actually, thinking about those 2 errors, I think this explanation is pretty likely. Without seeing your code I couldn't tell you where, but probably somewhere in main, game_manager, or somewhere like that if it's being called as soon as the Solarus logo menu finishes.