message code its not working with ModalPopupExtender

Hi 

in my page product page i have an icon allow users to send private message to the person who put the ads and this button is inside a listview and if the user click on then a ModalPopupExtender will appear with the message form but the send btn its not working very will can anybody help me with that, i have upload a screen record to make it easier to know my case 

https://www.youtube.com/watch?v=N6dxzvtZpus&feature=youtu.be

namespace beravoSV
{
    public partial class AdsDetails : System.Web.UI.Page
    {
       string cs = ConfigurationManager.ConnectionStrings["BeravaConnectionString"].ConnectionString.ToString();

        protected void Page_Load(object sender, EventArgs e)
        {
      
            SqlConnection showads = new SqlConnection(cs);
            SqlCommand CMDshowads = new SqlCommand("SELECT * FROM ads where AdsID = @AID", showads);
            SqlDataAdapter DAshowads = new SqlDataAdapter(CMDshowads);
            DataSet dsshowads = new DataSet();
            CMDshowads.Parameters.AddWithValue("@AID", Page.Request.QueryString["AID"].ToString());
            showads.Open();
            DAshowads.Fill(dsshowads,"ads");
            CMDshowads.ExecuteNonQuery();
            showads.Close();
            adsdetaillstview.DataSource = dsshowads;
            adsdetaillstview.DataBind();

        }

       

        protected void adsdetailview_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        protected void likebtn_Click(object sender, ImageClickEventArgs e)
        {

        }

        protected void Sndmailtoadder_Click(object sender, ImageClickEventArgs e)
        {
            if (Session["UsrNme"] != null)
            {
            SqlConnection Msgsqlcon = new SqlConnection(cs);
            SqlCommand Msgcmd = new SqlCommand();

            string sqlstatment = "INSERT INTO mails (AdsID, Mestitle, Message, UID, From, Date) VALUES (@AdsID,@Mestitle,@Message,@UID,@From,@Date)";

            Msgcmd.Connection = Msgsqlcon;
            Msgcmd.CommandType = CommandType.Text;
            Msgcmd.CommandText = sqlstatment;


            var adsnummsglbl = (Label)adsdetaillstview.FindControl("adsnummsglbl");
            var adstitmsglbl = (Label)adsdetaillstview.FindControl("adstitmsglbl");
            var adsmessagetxtbx = (Label)adsdetaillstview.FindControl("adsmessagetxtbx");
            var Reciverlblnme = (Label)adsdetaillstview.FindControl("Reciverlblnme");
            var passtxtbx2 = (Label)adsdetaillstview.FindControl("passtxtbx2");

            //Insert the parameters first
            Msgcmd.Parameters.AddWithValue("@AdsID", adsnummsglbl.Text);
            Msgcmd.Parameters.AddWithValue("@Mestitle", adstitmsglbl.Text);
            Msgcmd.Parameters.AddWithValue("@Message", adsmessagetxtbx.Text);
            Msgcmd.Parameters.AddWithValue("@UID", Reciverlblnme.Text);
            Msgcmd.Parameters.AddWithValue("@From", passtxtbx2.Text);
            Msgcmd.Parameters.AddWithValue("@Date", DateTime.Now);


            SqlDataAdapter DAMsg = new SqlDataAdapter(Msgcmd);
            DataSet DSMsg = new DataSet();
            DAMsg.SelectCommand = Msgcmd;
            DAMsg.Fill(DSMsg);
            //Session["UsrNme"] = UsrNme.Text;
            //Response.Redirect("User panel.aspx");
            }

        
            
            else
            {
                Response.Write("You have to login into your account to be able to send a message");
            }
        }

        protected void commentbtn_Click(object sender, ImageClickEventArgs e)
        {

        }
        
    }
}

<asp:ListView ID="adsdetaillstview" runat="server"><ItemTemplate><br /><br /><div class="iconadsbox2"><asp:ImageButton ID="likebtn" runat="server" 
                   ImageUrl="~/iconsimg/favoritestar2.png" OnClick="likebtn_Click" CausesValidation="false"/>&nbsp;&nbsp;&nbsp;<asp:ImageButton ID="Sndmailtoadder" runat="server" 
                   ImageUrl="~/iconsimg/mailposter.png" OnClick="Sndmailtoadder_Click" CausesValidation="false"/>&nbsp;&nbsp;&nbsp;</div><br /><br /><asp:Panel ID="adsshowmsgpanel" runat="server" BackColor="White" Width="500" Height="365" CssClass="pnpopup"><fieldset><legend>Send Message:</legend><table><tr><td>Ads Number:</td><td><asp:Label ID="adsnummsglbl" runat="server" Text='<%# Eval("AdsID") %>'></asp:Label></td></tr><tr><td>Ads Title:</td><td><asp:Label ID="adstitmsglbl" runat="server" Text='<%# Eval("AdsTit") %>'></asp:Label></td></tr><tr><td>
            From:&nbsp;&nbsp;</td><td><asp:Label ID="senderlblnme" runat="server" Text=""></asp:Label></td><br /></tr><tr><td>
            To:&nbsp;&nbsp;</td><td><asp:Label ID="Reciverlblnme" runat="server" Text='<%# Eval("UID") %>'></asp:Label></td></tr><tr><td>
            Your Message: &nbsp;&nbsp;</td><td><asp:TextBox ID="adsmessagetxtbx" runat="server" Height="200px" MaxLength="500" 
               Width="300px" TextMode="multiline"></asp:TextBox></td></tr><tr><td><asp:Button ID="Closebtn" runat="server" Text="Close" /></td><td> <asp:Button runat="server" ID="sendbtn" Text="Send"/></td></tr></table></fieldset></asp:Panel><asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server" PopupControlID="adsshowmsgpanel" TargetControlID="Sndmailtoadder" CancelControlID="Closebtn"></asp:ModalPopupExtender>


...... here the rest of page code .......
     
    
     </ItemTemplate></asp:ListView></asp:Content>