public void AlertMsg(string msg, bool async)

        {

            string script = string.Format("alert('{0}'); ", msg);

            RegisterClientScript(script, async);

 public void RegisterClientScript(string script, bool async)

        {

            if (async)

            {

                System.Web.UI.ScriptManager.RegisterStartupScript(this.Page, this.GetType(), Guid.NewGuid().ToString(), script, true);

            }

            else

            {

                this.Page.ClientScript.RegisterStartupScript(this.GetType(), Guid.NewGuid().ToString(), script, true);

            }

        }