webservices异步调用

下面是我的一段代码，用来调用WebServices,名称为myServices                    System.Threading.Thread webThread = new System.Threading.Thread(delegate()
                    {
                        myServices.ValidateLoginAsync(userName, userPwd);
                        myServices.ValidateLoginCompleted += new ValidateLoginCompletedEventHandler(myServices_ValidateLoginCompleted);
                    });
                    
                    webThread.Start();
下面这段代码，第一次执行一次，第二次他就执行了两边，逐渐增多，不知道是什么原因，希望大家帮忙看一下 void myTaxiEServices_ValidateLoginCompleted(object sender, ValidateLoginCompletedEventArgs e)
        {
if (e.Result.Length > 0)
                {
                 }
                else
                {
                   
                }
}