So, I tried to bake the normal map again, but still have the same result. Here is the link of my .blend file: https://www.dropbox.com/s/uroq4176zc69l4l/big_rock_textures.blend?dl=0
I packed the normal map into the .blend file.
I also get an error when baking the normal map: “Circular reference in texture stack”. So, I removed the material from the object and then baked it, but as I said I get no normal information.
Thank you very much for having a look!