There is no such file in my game. I have just tested every fight and I do not get an error like that. Can you be a bit more specific in regard to what enemy you were fighting, did you have the Bunny in your party? What actions did you take just before the fight?
Alternatively, try putting a random .png picture into that directory and giving it that name to see if it fixes it. However, no such file is supposed to exist in the first place.