Updating rotation of client not working - strange error

transform.rotation assign attempt for 'Player Multi(Clone)' is not valid. Input rotation is { NaN, NaN, NaN, NaN }. UnityEngine.Transform:set_rotation(Quaternion) PlayerTransformSync:LerpRotation() (at Assets/Scripts/PlayerTransformSync.cs:57) PlayerTransformSync:Update() (at Assets/Scripts/PlayerTransformSync.cs:26)

What does this mean? I have been trying to fix this for an hour, eventually I just gave in and decided to ask a question.

I tried several things, including changing how i rotate the player, etc.

Code:

 using UnityEngine;
 using UnityEngine.Networking;
 using System.Collections;
 
 public class PlayerTransformSync : NetworkBehaviour {
 
     [SyncVar]
     private Vector3 syncPos;
     [SyncVar]
     private Quaternion syncRot;
     [SerializeField]
     private float lerpRate;
     [SerializeField]
     private float moveThreshold;
     [SerializeField]
     private float angularThreshold;
     
     void Update () {
         if (isLocalPlayer)
         {
             TransmitTransform ();
         }
         else
         {
             LerpPosition ();
             LerpRotation ();
         }
     }
     
     [Command]
     void CmdProvidePositionToServer () {
         syncPos = transform.position;
     }
     
     [Command]
     void CmdProvideRotationToServer () {
         syncRot = transform.rotation;
     }
     
     [ClientCallback]
     void TransmitTransform () {
         if (Vector3.Distance (transform.position, syncPos) > moveThreshold)
         {
             CmdProvidePositionToServer ();
         }
         if (Quaternion.Angle (transform.rotation, syncRot) > angularThreshold)
         {
             CmdProvideRotationToServer ();
         }
     }
 
     void LerpPosition () {
         transform.position = Vector3.Lerp (transform.position, syncPos, lerpRate);
     }
     
     void LerpRotation () {
         transform.rotation = Quaternion.Lerp (transform.rotation, syncRot, lerpRate);
     }
 }