GUI Skin Button is missing when back from other scenes.

I try to create simple main menu. but the GUI Skin of one menu seems like not work, it become transparent but still work on click. Here is the script of that menu. those script is same as like as other menus that is not become transparent.

public class M_SKKD : MonoBehaviour { public GUISkin Skin; void Start () { } void Update () { } void OnGUI(){ float btnHeight = Screen.height*3/12; float btnWeight = btnHeight*47/50; float btnLeft = Screen.width/4-(btnWeight/2); float btnTop = Screen.height*2/5-(btnHeight/3); GUI.skin = Skin; if (GUI.Button(new Rect(btnLeft,btnTop,btnWeight,btnHeight),"")){ Application.LoadLevel("SKKD"); } } }

Is something wrong? :)