UnityException: You are not allowed to call this function when declaring a variable.
Move it to the line after without a variable declaration.
If you are using C# don't use this function in the constructor or field initializers, Instead move initialization to the Awake or Start function.

UnityEngine.GameObject.FindWithTag (System.String tag)
JumpFPC..ctor ()   (at Assets/JumpFPC.js:8)