Why is the blackboard value as object cast to third person character failing?

I just started learning Unreal Engine. I saw the Ian Shadden tutorial on AI where he uses a scene root component as pathnode for the ai character to follow. I decided to use that for the ai to follow player. so i changed the data type of variable that ai character stores as desirednode to thridpersoncharacter. and i also changed the cast of the blackboard value as object to third person character, which was earlier to path node. but is is not working due to some reason. can anyone pls help me with it. pls answer fast if possible.