Editor Button error (Multi-object editing not supported)

I want to create an editor button in my script to call some methods, and I’ve looked at tutorial on unity site how to do this, and i’ve made a class that derives from editor.

Here is my base class:

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

public class AntTowerDemo : MonoBehaviour {

    //public field, methods and stuff
}

and here is my editor class:

using UnityEngine;
using System.Collections;
using UnityEditor;

[CustomEditor(typeof(AntTowerDemo))]
public class AntTowerEditor : Editor
{

    public override void OnInspectorGUI()
    {
        DrawDefaultInspector();

        AntTowerDemo atd = (AntTowerDemo)target;
        if (GUILayout.Button("Save Ant Tower Data"))
            atd.SaveData();
    }
}

Problem is I get the error where I should see the class fields in Inspector, I see “Multi-object editing not supported”.

Also when I click on the GameObject containing the script I get an error “Instance of AntTowerEditor couldn’t be created because there is no script with that name.”

I’ve made sure that I have two separate scripts and even tried declaring editor extension class inside of AntTowerDemo class but I get the same error every time.

I’ve got 4.3.1 something Unity and as I see in that tutorial it says that it’s been tested in that Unity. Do I need Unity pro for this functionality?

Never mind I missed the fact that you need to put the extension class (in my case AntTowerEditor) into EDITOR FOLDER INSIDE PROJECT… What a dumb error… -.-