After having a look at the project I understand what the error you are seeing is. The array you have is of type “sphere blueprint”. While all “sphere blueprint” actors are actor blueprints, not all actor blueprints are “sphere blueprint”. You will have to confirm that the actor you hit is a sphere blueprint before you can set it to the array. To do this, drag off of hit actor and implement a “cast to sphere blueprint” node. You will want to do this before your add array. From the "As Sphere Blueprint C output pin, you can add, find, and get the actor as you have set up. The warning you are receiving is simply letting you know that “hit actor” is referring to any actor hit, not just sphere blueprints.