Hello,
Maxon introduced the “Magic Bullet Looks” plugin in Cinema 4D R25. What it does, is it allows its users to collor correct /adjust their renders. So lets say you have a scene which took 2 hours to render and you just realised that you wanted the lighting to be warmer or the scene to be darker/brighter. With Magic Bullet Looks you don’t have to rerender your scene or load your final image into Photoshop. You can do this and more inside Cinema 4D directly.
So the message you are seeing is mostly harmless.
How can you avoid this message:
1) Open Cinema 4D and load your scene.
2) Open render settings. (Ctrl+B for windows, ⌘ + B for Mac)
3) On the left list there is a “Magic Bullet Looks” entry.
4) Right click on that and select remove. You can also select it and press the “Delete” button on the keyboard.
Now if you save the scene, you should be good.