Modal POPup doesnt display

I have several modal popups that appear to work just fine. One, however does not. It is triggered by a button in a listview but when you press the button the list shia little but the popup does not show:

The html

<asp:ListView ID="lvMuttTrack" runat="server" OnItemDataBound="lvMuttTrack_ItemDataBound" 
                    style="width: 200px; margin: auto; margin-right: 20px; hieght: 50px; background-color: whitesmoke;"
                    GroupPlaceholderID="gpid"><LayoutTemplate><p><asp:PlaceHolder ID="gpid" runat="server" /></p></LayoutTemplate><GroupTemplate><ol><asp:PlaceHolder ID="itemPlaceholder" runat="server" /></ol></GroupTemplate><ItemTemplate><%-- <div style="height: 20px; width: 100%; overflow: auto;"> --%><asp:Panel ID="itemPlaceholder" runat="server" Width="150px" BackColor="black" Style="margin-bottom: 5px; align-items: center;"><table runat="server" id="tbldoglist" style="background-color: aliceblue; width: 150px; text-align: left;"><tr id="trdog"><td id="tddog"><asp:Image ID="idogg" runat="server" /></td><td id="td1" colspan="2"><asp:Label ID="bname" runat="server" Text='<%# Bind("dname") %>' Style="font-size: x-small; color: black; font-weight: 600;" /><br /><asp:HiddenField ID="hfrideid" runat="server" Value='<%# Bind("rideid")  %>' /><asp:HiddenField ID="hf" runat="server" Value='<%# Bind("riderid")  %>' /></td></tr><tr><td colspan="2"><asp:Label ID="Label2" runat="server" Text="Distance: " Style="font-size: x-small; color: darkslateblue;" /><asp:Label ID="Label3" runat="server" Text='<%# Bind("distance") %>' Style="font-size: x-small; color: darkslateblue;" /><br /><asp:Label ID="Label10" runat="server" Text="Time: " Style="font-size: x-small; color: darkslateblue;" /><asp:Label ID="lblhr" runat="server" Text='<%# Bind("hours") %>' Style="font-size: x-small; color: darkslateblue;" /><asp:Label ID="Label7" runat="server" Text=" H " Style="font-size: x-small; color: darkslateblue;" /><asp:Label ID="Label8" runat="server" Text='<%# Bind("minutes") %>' Style="font-size: x-small; color: darkslateblue;" /><asp:Label ID="Label9" runat="server" Text=" M " Style="font-size: x-small; color: darkslateblue;" /><br /><asp:Label ID="Label13" runat="server" Text='<%# Bind("gain") %>' Style="font-size: x-small; color: darkslateblue;" /></td></tr><tr><td colspan="2"><div><asp:Repeater ID="rptreply" runat="server"><ItemTemplate><asp:Label ID="dnameLabel" runat="server" Font-Size="X-Small"
                                                        Font-Bold="true" ForeColor="Firebrick" Text='<%# DataBinder.Eval(Container.DataItem, "[\"dname\"]")%>' /><div id="div1" runat="server" class="replydiv"><asp:Label ID="colon" runat="server" Font-Size="X-Small" Text=": " /><asp:TextBox ID="tbreply" runat="server" Font-Size="X-Small" Text='<%# Bind("replytext") %>'
                                                            TextMode="MultiLine" Height="40"
                                                            Style="border-style: solid; border-width: 1px; border-color: antiquewhite;" /><%--<asp:Label ID="replytextLabel" runat="server" Font-Size="X-Small" Text='<%# Bind("replytext") %>' />--%><br /></div></ItemTemplate><AlternatingItemTemplate><div id="div2" runat="server" class="replyalt" /><asp:Label ID="dnameLabela" runat="server" Font-Size="X-Small" Font-Bold="true" ForeColor="Firebrick" Text='<%# DataBinder.Eval(Container.DataItem, "[\"dname\"]")%>' /><asp:Label ID="colona" runat="server" Font-Size="X-Small" Text=": "> </asp:Label><asp:TextBox ID="tbreply" runat="server" Font-Size="X-Small" Text='<%# Bind("replytext") %>' TextMode="MultiLine" Height="30" Style="border-style: solid; border-width: 1px; border-color: antiquewhite;"></asp:TextBox><%--<asp:Label ID="replytextLabela" runat="server" Font-Size="X-Small" Text='<%# Bind("replytext") %>' />--%></div></AlternatingItemTemplate></asp:Repeater></div><asp:ImageButton ID="btnComment" runat="server" ImageUrl="~/Images/Icons/comment.png"
                                            CommandName="Open" ToolTip="Comment on this Post" CommandArgument='<%# Eval("rideid") %>' /><%--    <asp:ImageButton ID="btncommment" runat="server" ImageUrl="~/Images/Icons/comment.png" />--%><asp:ImageButton ID="btnBone" runat="server" ImageUrl="~/Images/Icons/bone.png" ToolTip="Throw this Dog a Bone!" /><asp:Label ID="lbbc" runat="server"></asp:Label><asp:Label ID="hlbone" runat="server"></asp:Label></td></tr><tr><td><asp:ImageButton ID="imgnew" runat="server" OnClick="imgnew_Click" /></td><td></td><td></td></tr></table></asp:Panel></ItemTemplate><EmptyDataTemplate><div><asp:Label ID="lblzero" runat="server" Text=" No data try another month."></asp:Label></div></EmptyDataTemplate></asp:ListView><asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:BDUCConnectionString %>" SelectCommand="um_muttTracker" SelectCommandType="StoredProcedure"><SelectParameters><asp:Parameter Name="riderid" Type="Int32" /></SelectParameters></asp:SqlDataSource></div></div><div style="background-color: darkgray; border-width: .9em; color: ghostwhite; width: 300px; float: left; font-weight: 600; border-color: gainsboro; border-style: solid; border-width: 1px; margin-left: 28px; margin-top: 20px; text-align: center; width: 29%; height: 400px;"><div><asp:Button ID="Button4" runat="server" OnClick="Button4_Click" Text="Button" /></div></div><div style="background-color: darkslateblue; border-width: .9em; color: ghostwhite; width: 300px; float: left; font-weight: 600; border-color: gainsboro; border-style: solid; border-width: 1px; margin-left: 28px; margin-top: 20px; text-align: center; width: 29%; height: 400px;"></div></div><div><asp:Panel ID="Panel1" runat="server" Style="display: none;"><asp:Label ID="lblcmy" runat="server" Text="Enter Comment (200 characters max.)" /><br><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></asp:Panel><asp:Button ID="Button1" runat="server" Text="Button" Style="display: none;" /><ajaxToolkit:ModalPopupExtender ID="Panel1_ModalPopupExtender" runat="server" 
            Enabled="True" TargetControlID="Button1"
            BackgroundCssClass="modalBackground" PopupControlID="Panel1"></ajaxToolkit:ModalPopupExtender></div>
the code:

    protected void imgnew_Click(object sender, ImageClickEventArgs e)
    {
        Panel1_ModalPopupExtender.Show();
    }

THanks...