Why is playerControllerId = -1

Line 94 -- Just debugging and trying to find out why the camera isn't setting the target as the latest player to spawn

 using System;
 using UnityEngine;
 using UnityEngine.Networking;
 
 namespace UnityStandardAssets.Cameras
 {
     public abstract class AbstractTargetFollower : NetworkBehaviour
     {
         public enum UpdateType // The available methods of updating are:
         {
             FixedUpdate, // Update in FixedUpdate (for tracking rigidbodies).
             LateUpdate, // Update in LateUpdate. (for tracking objects that are moved in Update)
             ManualUpdate, // user must call to update camera
         }
 
         [SerializeField] protected Transform m_Target;            // The target object to follow
         [SerializeField] private bool m_AutoTargetPlayer = true;  // Whether the rig should automatically target the player.
         [SerializeField] private UpdateType m_UpdateType;         // stores the selected update type
 
         protected Rigidbody targetRigidbody;
 
 
         protected virtual void Start()
         {
 
                 // if auto targeting is used, find the object tagged "Player"
                 // any class inheriting from this should call base.Start() to perform this action!
                 if (m_AutoTargetPlayer)
                 {
                     FindAndTargetPlayer();
                 }
                 if (m_Target == null) return;
                 targetRigidbody = m_Target.GetComponent<Rigidbody>();
 
         }
 
 
         private void FixedUpdate()
         {
 
                 // we update from here if updatetype is set to Fixed, or in auto mode,
                 // if the target has a rigidbody, and isn't kinematic.
                 if (m_AutoTargetPlayer && (m_Target == null || !m_Target.gameObject.activeSelf))
                 {
                     FindAndTargetPlayer();
                 }
                 if (m_UpdateType == UpdateType.FixedUpdate)
                 {
                     FollowTarget(Time.deltaTime);
                 }
         }
 
 
         private void LateUpdate()
         {
 
                 // we update from here if updatetype is set to Late, or in auto mode,
                 // if the target does not have a rigidbody, or - does have a rigidbody but is set to kinematic.
                 if (m_AutoTargetPlayer && (m_Target == null || !m_Target.gameObject.activeSelf))
                 {
                     FindAndTargetPlayer();
                 }
                 if (m_UpdateType == UpdateType.LateUpdate)
                 {
                     FollowTarget(Time.deltaTime);
                 }
 
         }
 
 
         public void ManualUpdate()
         {
 
                 // we update from here if updatetype is set to Late, or in auto mode,
                 // if the target does not have a rigidbody, or - does have a rigidbody but is set to kinematic.
                 if (m_AutoTargetPlayer && (m_Target == null || !m_Target.gameObject.activeSelf))
                 {
                     FindAndTargetPlayer();
                 }
                 if (m_UpdateType == UpdateType.ManualUpdate)
                 {
                     FollowTarget(Time.deltaTime);
                 }
 
         }
 
         protected abstract void FollowTarget(float deltaTime);
 
 
         public void FindAndTargetPlayer()
         {
             
             if (this.isLocalPlayer) {
                 Debug.Log("playerControllerId = " + playerControllerId);
             }
 
             var targetObj = GameObject.FindGameObjectWithTag("Player");
 
             if (targetObj)
             {
                 //SetTarget(targetObj.transform);
                 SetTarget(targetObj.transform);
             }
 
         }
 
 
         public virtual void SetTarget(Transform newTransform)
         {
             m_Target = newTransform;
         }
 
 
         public Transform Target
         {
             
             get { return m_Target; }
         }
 
     }
 }
 

If a client didn't add any player, the NetworkBehaviour.playerControllerId is -1 as default .(Yes, the default value of playerControllerId is -1, not 0. You can try not adding a player when you connect to the server and print(playerControllerId) to check this.)

If you have ever used ClientScene.AddPlayer(short playerControllerId) to spawn a new player for the client, the playerControllerId shouldn't be -1.

How did you spawn your Player? Or have you ever removed the player? Or you just didn't add one?