Script controls may not be registered before PreRender

Place the code in the code behind and run

protected override void OnInit(EventArgs e)
{

if (ScriptManager.GetCurrent(this.Page) == null)

{
scriptManager = new ScriptManager();
scriptManager.ID = “myScriptManager”;
scriptManager.EnablePartialRendering = true;
this.Page.Form.Controls.Add(scriptManager);

}

base.OnInit(e);
}