Access Denied, when trying to create a png in an editor extension

I get an UnauthorizedAccessException when trying to create a png in an editor extension when using File.WriteAllBytes(), but only like this:

     Texture2D SaveMap(Texture2D map, string path)
     {
         byte[] pngShot = map.EncodeToPNG();
         File.WriteAllBytes(Application.dataPath + "/" + path, pngShot);
         Debug.Log(Application.dataPath + "/" + path);
 
         AssetDatabase.ImportAsset("Assets/" + path);
         TextureImporter textureImporter = TextureImporter.GetAtPath("Assets/" + path) as TextureImporter;
         TextureImporterSettings st = new TextureImporterSettings();
         textureImporter.ReadTextureSettings(st);
         st.wrapMode = TextureWrapMode.Clamp;
         textureImporter.wrapMode = TextureWrapMode.Clamp;
         st.readable = true;
         textureImporter.SetTextureSettings(st);
         AssetDatabase.ImportAsset("Assets/" + path);
         return AssetDatabase.LoadAssetAtPath("Assets/" + path, typeof(Texture2D)) as Texture2D;
     }
     public Texture2D SaveMap(string name, Texture2D map)
     {
         string fullpath = path + "/" + gameObject.name + "_" + name + ".png";
         Helper.CreateFoldersIfNecessary(fullpath);
 
         byte[] pngShot = map.EncodeToPNG();
         File.WriteAllBytes(Application.dataPath + "/" + fullpath, pngShot);
 
         AssetDatabase.ImportAsset("Assets/" + fullpath);
         TextureImporter textureImporter = TextureImporter.GetAtPath("Assets/" + fullpath) as TextureImporter;
         TextureImporterSettings st = new TextureImporterSettings();
         textureImporter.ReadTextureSettings(st);
         st.wrapMode = TextureWrapMode.Clamp;
         textureImporter.wrapMode = TextureWrapMode.Clamp;
         st.readable = true;
         textureImporter.SetTextureSettings(st);
         AssetDatabase.ImportAsset("Assets/" + fullpath);
         return AssetDatabase.LoadAssetAtPath("Assets/" + fullpath, typeof(Texture2D)) as Texture2D;
     }

the upper function is called from inside this class, and works, the lower function is called from an other script, and throws the exception.

I really don't get why.