dropdownlist doesnt trick on host

while i use my local host dropdownlist's tricks work well  
but  when i try to use on my host , dropdownlist's Selected index change event doesnt trick

 

<asp:DropDownList ID="dropCountry" BackColor=White CssClass="libox" runat="server" AutoPostBack="True" OnSelectedIndexChanged="dropCountry_SelectedIndexChanged"></asp:DropDownList>

   protected void dropCountry_SelectedIndexChanged(object sender, EventArgs e)
        {
            lbl2.Text = "annen";
            dropCity.Items.Clear();
            cityService.GlobalWeather cityServ = new cityService.GlobalWeather();
            string result = cityServ.GetCitiesByCountry(dropCountry.SelectedItem.Text);
            XDocument xdoc = XDocument.Parse(result);
            var citys  = xdoc.Descendants("Table");
            foreach (var tag in citys)
            {
                dropCity.Items.Add(tag.Element("City").Value);
            }
        }

Thanks..