Character Blueprint is PAWN, for it to work you need get player pawn
Probably You also have Player Controller blueprint somewhere.
Get Player controller >> you can cast to Controller type blueprint
Get Player Pawn >> you can cast to player character blueprint
Ps error code says exactly that. Look what class “Ghost_Bp” inherits from.
Also it is nice to have some naming convention for your blueprints.
For eg I am always naming my blueprints like this: BP_Ghost_Controller, BP_Ghost_Character etc.
When i want cast to any of my bps i write BP_ and i get list of all of my blueprints
When i need PAWN i just write _pawn or _Character etc.
That helps a lot.