Hey ,
When I play a slightly older version of your project converted to 4.6, it looks like Fireball_BP is not moving; they just sit there where spawned until their lifetime ends. I was able to fix this by simply duplicating ProjectileMovement component, deleting original component (Fireball_ProjectileMovement), and replacing call to component in Down Spawn Fireball function inside Fireball_Spawner_BP.
I don’t get error you posted an image of, though I suspect it’s simply because I’m using an older version of your project. Try duplicating/replacing that component and let me know if there are still errors after that. I’m going to look into this a bit further and enter a bug if we both see same thing. Thanks!