Network spawning not working

So i'm building a line wars game, and i have run into a problem where i can instantiate and spawn the object on the local client, and i synchronizes perfectly.. But when i do it on the remote client, it only instantiates and doesn't spawn on the server, i get this error:

SpawnObject for MeleeHouse(Clone) (UnityEngine.GameObject), NetworkServer is not active. Cannot spawn objects without an active server.

I have another object tell the manager to spawn the bulding at it's transform. it looks like this:

    using UnityEngine;
    using System.Collections;
    public class BuldingPlatformScript : MonoBehaviour {

 Color defaultColor;
 public Color highlightColor;
 GameObject graphicGO;

 void Start(){
     graphicGO = transform.GetChild (0).gameObject;
     defaultColor = graphicGO.GetComponent<Renderer> ().material.color;
 }

 void OnMouseEnter (){
     graphicGO.GetComponent<Renderer> ().material.color = highlightColor;
 }

 void OnMouseExit (){
     graphicGO.GetComponent<Renderer> ().material.color = defaultColor;
 }

 void OnMouseUp () {
     GameObject.Find ("_Scripts_").GetComponent<BuildingManager> ().MakeBuilding (transform);
 }

}

and the manager script looks like this..

    using UnityEngine;
    using UnityEngine.Networking;
    using System.Collections;
    public class BuildingManager : NetworkBehaviour {
 
 int currentMoney = 50;
 GameObject selectedBuildingGO;
 int selectedBuildingPrize = 0;

 public bool isMenuOpen = false;
 public GameObject menuGO;

 int belongsToPlayer = 0;

 Transform target;

 public void GetPlayerNumber (int playerNumber) {
     belongsToPlayer = playerNumber;
 }

 //Activated by a UI button
 public void SetSelectedBuilding (GameObject building){
     selectedBuildingGO = building;
 }

 //Activated by a UI button
 public void SetBuildingPrize (int sentPrice){
     selectedBuildingPrize = sentPrice;
 }

 //Activated by a buildingPlatform
 public void MakeBuilding (Transform targetPlatform){
     if (!isClient)
         return;

     if (currentMoney >= selectedBuildingPrize) {
         target = targetPlatform;
         currentMoney -= selectedBuildingPrize;
         GameObject building = Instantiate (selectedBuildingGO, target.position, Quaternion.identity)as GameObject;
         Destroy(target.gameObject);
         building.tag = "Team"+belongsToPlayer+"";
         NetworkServer.Spawn(building);
     } else {
         //DO: show you dont have enough money
     }
 }

 void Update(){
     //Check if to open the buildingmenu
     if (Input.GetKeyUp (KeyCode.B)) {
         if(isMenuOpen == false){
             menuGO.SetActive(true);
             isMenuOpen = true;
         }else{
             menuGO.SetActive(false);
             isMenuOpen = false;
         }
     }

     if (isMenuOpen == true) {
         isMenuOpen = menuGO.activeInHierarchy;
     }
 }

}