Why is My spawner Not working? I have listed the error below.

Questions & Answers
1

Error “SetDestination” can only be called on an active agent that has been placed on a NavMesh. UnityEngine.AI.NavMeshAgent:SetDestination(Vector3) Enemy_Controller:Update() (at Assets/Scripts/Enemy/Enemy_Controller.cs:28)

I have put the enemy controller script first and the enemy spawner second.

This Is My Enemy Controller Script:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.AI;

public class Enemy_Controller : MonoBehaviour
{

public float lookradius = 10f;
Transform target;
NavMeshAgent agent;

// Use this for initialization
void Start()
{
    target = PlayerManager.instance.player.transform;
    agent = GetComponent<NavMeshAgent>();
}

// Update is called once per frame
void Update()
{
    float distance = Vector3.Distance(target.position, transform.position);

    if (distance <= lookradius)
    {
        agent.SetDestination(target.position);

        if (distance <= agent.stoppingDistance)
        {
            //atack target
            FaceTarget();
        }
    }
}

void FaceTarget()
{
    Vector3 direction = (target.position - transform.position).normalized;
    Quaternion lookrotation = Quaternion.LookRotation(new Vector3(direction.x, 0, direction.z));
    transform.rotation = Quaternion.Slerp(transform.rotation, lookrotation, Time.deltaTime * 5f);
}

void OnDrawGizmosSelected()
{
    Gizmos.color = Color.red;
    Gizmos.DrawWireSphere(transform.position, lookradius);

}

}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Spawner : MonoBehaviour {

public GameObject spawn;
public bool stopSpawning = false;
public float spawnTime;
public float spawnDelay;

// Use this for initialization
void Start () {
    InvokeRepeating("SpawnObject", spawnTime, spawnDelay);
}

public void SpawnObject()
{
    Instantiate(spawn, transform.position, transform.rotation);
    if (stopSpawning)
    {
        CancelInvoke("SpawnObject");
    }
}

}

2

As the exception says you’re trying to call SetDestination before the agent has been initialized and placed on the navmesh, to fix this you can add a check in Update of Enemy_Controller:

void Update()
{
        if (agent.isActiveAndEnabled && agent.isOnNavMesh)
        {
                // Do stuff here...
        }
}