asp.net删除AD用户信息失败原因求救.

用如下.net代码删除域用户信息失败,请高手指点.
String strLDAP = "LDAP://domName/CN=users,DC=domName,DC=com";
            DirectoryEntry org, usrEnt;
            org = new DirectoryEntry(strLDAP, "userName", "pwd", AuthenticationTypes.Secure);//模拟管理员帐号和密码
            string LoginNum = "123456";//用户登录名
            usrEnt = org.Children.Find("CN=" + LoginNum , "User");//找到用户
            org.Children.Remove(usrEnt);//删除