Problem on Behavior tree: Observer abort both option

Yeah, right! I start play, and the enemy pawn I placed just does not move. When I hit Esc to stop the game, a pop up notifies me about the error.
Here’s the blueprint, seems that the error is caused by the “get controlled pawn” node.

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I don’t know how to solve that, the blueprint is the same as the tutorial’s one so I can’t even figure out where to modify it.
The first time I tried to build this AI was on a random Top Down template, and it worked on the first try. Then I re-built it on a copy of our project, and I met two problems: this one (exactly the same error) and the observer abort I explained above. I solved the first one just copy-and-pasting the entire “follower Ai CON” bp from my Top Down template, and it worked, but instead I didn’t succeded on solving the observer abort problem. Anyway, I builted a third time the AI on our real project, with a friend of mine who’s working with me. The observer abort’s problem did not showed up, everything was fine, exept for this error; this time the “copy and paste” strategy didn’t work.