Modal Polpup Closes immediately

I have a formview with client information displayed. A    modal popup is supposed to show a form to update that information. However when I click the button the popup flasheds opened and closed in a fraction of a second.

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"><div id="blkdiv" class="blackpages"><div><div><div style="float:left; width:340px; height:250px; border:1px dashed gray; margin-top:25px;"><asp:FormView ID="FormView1" runat="server" DataKeyNames="riderid" ForeColor="WhiteSmoke"><EditItemTemplate>
                    titleid:<asp:TextBox ID="titleidTextBox" runat="server" Text='<%# Bind("titleid") %>' /><br />
                    fname:<asp:TextBox ID="fnameTextBox" runat="server" Text='<%# Bind("fname") %>' /><br />
                    mname:<asp:TextBox ID="mnameTextBox" runat="server" Text='<%# Bind("mname") %>' /><br />
                    lname:<asp:TextBox ID="lnameTextBox" runat="server" Text='<%# Bind("lname") %>' /><br />
                    suffixid:<asp:TextBox ID="suffixidTextBox" runat="server" Text='<%# Bind("suffixid") %>' /><br />
                    dname:<asp:TextBox ID="dnameTextBox" runat="server" Text='<%# Bind("dname") %>' /><br />
                    dob:<asp:TextBox ID="dobTextBox" runat="server" Text='<%# Bind("dob") %>' /><br />
                    gender:<asp:TextBox ID="genderTextBox" runat="server" Text='<%# Bind("gender") %>' /><br />
                    comment:<asp:TextBox ID="commentTextBox" runat="server" Text='<%# Bind("comment") %>' /><br />
                    riderid:<asp:Label ID="rideridLabel1" runat="server" Text='<%# Eval("riderid") %>' /><br /><asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" CommandName="Update" Text="Update" />&nbsp;<asp:LinkButton ID="UpdateCancelButton" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel" /></EditItemTemplate><InsertItemTemplate>
                    titleid:<asp:TextBox ID="titleidTextBox" runat="server" Text='<%# Bind("titleid") %>' /><br />
                    fname:<asp:TextBox ID="fnameTextBox" runat="server" Text='<%# Bind("fname") %>' /><br />
                    mname:<asp:TextBox ID="mnameTextBox" runat="server" Text='<%# Bind("mname") %>' /><br />
                    lname:<asp:TextBox ID="lnameTextBox" runat="server" Text='<%# Bind("lname") %>' /><br />
                    suffixid:<asp:TextBox ID="suffixidTextBox" runat="server" Text='<%# Bind("suffixid") %>' /><br />
                    dname:<asp:TextBox ID="dnameTextBox" runat="server" Text='<%# Bind("dname") %>' /><br />
                    dob:<asp:TextBox ID="dobTextBox" runat="server" Text='<%# Bind("dob") %>' /><br />
                    gender:<asp:TextBox ID="genderTextBox" runat="server" Text='<%# Bind("gender") %>' /><br />
                    comment:<asp:TextBox ID="commentTextBox" runat="server" Text='<%# Bind("comment") %>' /><br /><asp:LinkButton ID="InsertButton" runat="server" CausesValidation="True" CommandName="Insert" Text="Insert" />&nbsp;<asp:LinkButton ID="InsertCancelButton" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel" /></InsertItemTemplate><ItemTemplate>
                    titleid:<asp:Label ID="titleidLabel" runat="server" Text='<%# Bind("titleid") %>' /><br />
                    fname:<asp:Label ID="fnameLabel" runat="server" Text='<%# Bind("fname") %>' /><br />
                    mname:<asp:Label ID="mnameLabel" runat="server" Text='<%# Bind("mname") %>' /><br />
                    lname:<asp:Label ID="lnameLabel" runat="server" Text='<%# Bind("lname") %>' /><br />
                    suffixid:<asp:Label ID="suffixidLabel" runat="server" Text='<%# Bind("suffixid") %>' /><br />
                    dname:<asp:Label ID="dnameLabel" runat="server" Text='<%# Bind("dname") %>' /><br />
                    dob:<asp:Label ID="dobLabel" runat="server" Text='<%# Bind("dob") %>' /><br />
                    gender:<asp:Label ID="genderLabel" runat="server" Text='<%# Bind("gender") %>' /><br />
                    comment:<asp:Label ID="commentLabel" runat="server" Text='<%# Bind("comment") %>' /><br />
                    riderid:<asp:Label ID="rideridLabel" runat="server" Text='<%# Eval("riderid") %>' /><br /><asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="Button" CausesValidation="False" /><br /></ItemTemplate></asp:FormView><asp:SqlDataSource ID="dsdisplayrider" runat="server" ConnectionString="<%$ ConnectionStrings:BDUCConnectionString %>" SelectCommand="um_fetchridereditdata" SelectCommandType="StoredProcedure"><SelectParameters><asp:Parameter Name="rider" Type="Int32" /></SelectParameters></asp:SqlDataSource></div><div style="float:left; width:340px; border:1px dashed aqua; height:250px; margin-left:15px; margin-top:25px;"><asp:Label ID="Label3" runat="server" Font-Bold="true" Font-Size="Large" ForeColor="White" Text="Pookiewanna"></asp:Label></div><asp:SqlDataSource ID="dsRider" runat="server" ConnectionString="<%$ ConnectionStrings:BDUCConnectionString %>" SelectCommand="um_updateriderinfo" SelectCommandType="StoredProcedure" UpdateCommand="um_updateriderinfo" UpdateCommandType="StoredProcedure"><SelectParameters><asp:Parameter Name="riderid" Type="Int32" /><asp:Parameter Name="titleid" Type="Int32" /><asp:Parameter Name="fname" Type="String" /><asp:Parameter Name="lname" Type="String" /><asp:Parameter Name="mname" Type="String" /><asp:Parameter Name="suffixid" Type="Int32" /><asp:Parameter Name="dob" Type="DateTime" /><asp:Parameter Name="gender" Type="String" /><asp:Parameter Name="dname" Type="String" /><asp:Parameter Name="comment" Type="String" /></SelectParameters><UpdateParameters><asp:Parameter Name="riderid" Type="Int32" /><asp:Parameter Name="titleid" Type="Int32" /><asp:Parameter Name="fname" Type="String" /><asp:Parameter Name="lname" Type="String" /><asp:Parameter Name="mname" Type="String" /><asp:Parameter Name="suffixid" Type="Int32" /><asp:Parameter Name="dob" Type="DateTime" /><asp:Parameter Name="gender" Type="String" /><asp:Parameter Name="dname" Type="String" /><asp:Parameter Name="comment" Type="String" /></UpdateParameters></asp:SqlDataSource></div><asp:Panel ID="pnledit" runat="server" CssClass="gainsPanel" Width="270px"><asp:FormView ID="fveditrider" runat="server" DataKeyNames="riderid" DefaultMode="Edit" ForeColor="WhiteSmoke" Width="250" BackColor="Black"><EditItemTemplate>
                    titleid:<asp:TextBox ID="titleidTextBox" runat="server" Text='<%# Bind("titleid") %>' /><br />
                    fname:<asp:TextBox ID="fnameTextBox" runat="server" Text='<%# Bind("fname") %>' /><br />
                    mname:<asp:TextBox ID="mnameTextBox" runat="server" Text='<%# Bind("mname") %>' /><br />
                    lname:<asp:TextBox ID="lnameTextBox" runat="server" Text='<%# Bind("lname") %>' /><br />
                    suffixid:<asp:TextBox ID="suffixidTextBox" runat="server" Text='<%# Bind("suffixid") %>' /><br />
                    dname:<asp:TextBox ID="dnameTextBox" runat="server" Text='<%# Bind("dname") %>' /><br />
                    dob:<asp:TextBox ID="dobTextBox" runat="server" Text='<%# Bind("dob") %>' /><br />
                    gender:<asp:TextBox ID="genderTextBox" runat="server" Text='<%# Bind("gender") %>' /><br />
                    comment:<asp:TextBox ID="commentTextBox" runat="server" Text='<%# Bind("comment") %>' /><br />
                    riderid:<asp:Label ID="rideridLabel1" runat="server" Text='<%# Eval("riderid") %>' /><br /><asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" CommandName="Update" Text="Update" />&nbsp;<asp:LinkButton ID="UpdateCancelButton" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel" /></EditItemTemplate><ItemTemplate>
                    titleid:<asp:Label ID="titleidLabel" runat="server" Text='<%# Bind("titleid") %>' /><br />
                    fname:<asp:Label ID="fnameLabel" runat="server" Text='<%# Bind("fname") %>' /><br />
                    mname:<asp:Label ID="mnameLabel" runat="server" Text='<%# Bind("mname") %>' /><br />
                    lname:<asp:Label ID="lnameLabel" runat="server" Text='<%# Bind("lname") %>' /><br />
                    suffixid:<asp:Label ID="suffixidLabel" runat="server" Text='<%# Bind("suffixid") %>' /><br />
                    dname:<asp:Label ID="dnameLabel" runat="server" Text='<%# Bind("dname") %>' /><br />
                    dob:<asp:Label ID="dobLabel" runat="server" Text='<%# Bind("dob") %>' /><br />
                    gender:<asp:Label ID="genderLabel" runat="server" Text='<%# Bind("gender") %>' /><br />
                    comment:<asp:Label ID="commentLabel" runat="server" Text='<%# Bind("comment") %>' /><br />
                    riderid:<asp:Label ID="rideridLabel" runat="server" Text='<%# Eval("riderid") %>' /><br /><asp:LinkButton ID="EditButton" runat="server" CausesValidation="False" CommandName="Edit" Text="Edit" /></ItemTemplate></asp:FormView><asp:SqlDataSource ID="dseditrider" runat="server" ConnectionString="<%$ ConnectionStrings:BDUCConnectionString %>" SelectCommand="um_fetchridereditdata" SelectCommandType="StoredProcedure" UpdateCommand="um_updateriderinfo" UpdateCommandType="StoredProcedure"><SelectParameters><asp:Parameter Name="rider" Type="Int32" /></SelectParameters><UpdateParameters><asp:Parameter Name="riderid" Type="Int32" /><asp:Parameter Name="titleid" Type="Int32" /><asp:Parameter Name="fname" Type="String" /><asp:Parameter Name="lname" Type="String" /><asp:Parameter Name="mname" Type="String" /><asp:Parameter Name="suffixid" Type="Int32" /><asp:Parameter Name="dob" Type="DateTime" /><asp:Parameter Name="gender" Type="String" /><asp:Parameter Name="dname" Type="String" /><asp:Parameter Name="comment" Type="String" /></UpdateParameters></asp:SqlDataSource></asp:Panel><ajaxToolkit:ModalPopupExtender ID="pnledit_ModalPopupExtender" runat="server" BehaviorID="pnledit_ModalPopupExtender" 
             TargetControlID="pnlopen" PopupControlID="pnledit" BackgroundCssClass="modalBackground" CancelControlID="UpdateCancelButton"></ajaxToolkit:ModalPopupExtender> <asp:Button ID="pnlopen" runat="server" Text="Button" style="display:none;" /></div></div></asp:Content>

C#

using System;
using System.Collections.Generic;
using System.Data;

using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Profile_MyProfiles : System.Web.UI.Page
{
    int rid;
    protected void Page_Load(object sender, EventArgs e)
    {
       if (!IsPostBack)
       {
            rid = Convert.ToInt32(Session["RID"]);
            rider rd = new rider();
            FormView1.DataSource = rd.ridereditdata(rid);
            FormView1.DataBind();
        }
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        rider rd = new rider();
        fveditrider.DataSource = rd.getrider(rid);
        fveditrider.DataBind();
        pnledit_ModalPopupExtender.Show();
    }
}