Is Manager.js your script?
The method signature tells you what parameter types to use:
public static PlayMakerFSM FindFsmOnGameObject(GameObject go, string fsmName)
So the first parameter is a GameObject reference. GameObject.Find returns a GameObject reference, or you could use public GameObject variables that you assign at edit time.
If FindFsmOnGameObject cannot find the fsm it returns null, and then fsm.enabled=false would give you a NullReferenceException.
You need to track down why the return is null, e.g., the GameObject name is wrong, or the FSM name is wrong.
Note, GameObject.Find also only returns active GameObjects:
http://docs.unity3d.com/ScriptReference/GameObject.Find.htmlMaybe one of the GameObjects is not active...? You basically have to debug the code and figure out exactly where it is failing...