You need to plug in the execution pins of the Get All Actors of Class node 
The input execution pin to the On See event and the output execution pin to the Cast To node. Also just choose the enemy blueprint itself instead of the base one.
You need to plug in the execution pins of the Get All Actors of Class node
The input execution pin to the On See event and the output execution pin to the Cast To node. Also just choose the enemy blueprint itself instead of the base one.