Adding a Custom Button to the Inspector

Hi, i want to write an importer Script with a button in the Inspector. But i get allways the Message "multi-object editing not supported" and the only thing that i selected was the GameObjekt with the Script attached.

I have tested these example (Link) but i got the same Message.

Edit:

ObjectBuilderScript:

 using UnityEngine;
 using System.Collections;
 
 
 [AddComponentMenu("Tiled Map/Tiled Map Component")]
 public class ObjectBuilderScript : MonoBehaviour 
 {
     public GameObject obj;
     public Vector3 spawnPoint;
 
     public void BuildObject()
     {
         Instantiate(obj, spawnPoint, Quaternion.identity);
     }
 }

ObjectBuilderEditor:

 using UnityEngine;
 using System.Collections;
 using UnityEditor;
 
 [CustomEditor(typeof(ObjectBuilderScript))]
 public class ObjectBuilderEditor : Editor
 {
     public override void OnInspectorGUI()
     {
         DrawDefaultInspector();
 
         ObjectBuilderScript myScript = (ObjectBuilderScript)target;
         if(GUILayout.Button("Build Object"))
         {
             myScript.BuildObject();
         }
     }
 }