Error Message

Question

Hi

   I have below Modal Popup. I want if From Date < Date of Request then message in Modal Popup should appear. It should not go back to previous page.

<div class="form-horizontal">
                                    <div class="modal-body">
                                        <div class="row">
                                            <div class="col-lg-6">
                                                <div class="form-group">
                                                    <asp:DropDownList ID="ddlMentor" class="form-control" required="true" parsley-trigger="change" AutoPostBack="true" OnSelectedIndexChanged="ddlMentor_SelectedIndexChanged" runat="server">
                                                        <asp:ListItem Value="">Select Mentor</asp:ListItem>
                                                    </asp:DropDownList>
                                                </div>
                                            </div>

                                            <div class="col-lg-6">
                                            <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                                               <ContentTemplate>
                                                    <%--<div class="col-lg-6">--%>
                                                        <div class="form-group">
                                                            <asp:DropDownList ID="ddlStudent" class="form-control" required="true" EnableViewState="false" parsley-trigger="change" runat="server">
                                                                <asp:ListItem Value="">Select Student</asp:ListItem>
                                                            </asp:DropDownList>
                                                        </div>
                                                    <%--</div>  --%>                                
                                               </ContentTemplate>
                                               <Triggers>
                                               <asp:AsyncPostBackTrigger ControlID="ddlMentor" EventName="SelectedIndexChanged" />
                                               </Triggers>
                                            </asp:UpdatePanel>
                                            </div>  

                                            <div class="col-lg-6">
                                                <div class="form-group">
                                                    <label>Date Of Request</label>&nbsp;<span style="color: red">*</span>
                                                    <asp:TextBox ID="txtDateOfRequest" class="form-control daterange-single" required="true" onkeydown="return false" placeholder="Date of Request" runat="server"></asp:TextBox>
                                                </div>
                                            </div>
                                            <div class="col-lg-6">
                                                <div class="form-group">
                                                    <label>Start Date</label>&nbsp;<span style="color: red">*</span>
                                                    <asp:TextBox ID="txtStartDate" class="form-control daterange-single" required="true" onkeydown="return false" placeholder="Start Date" runat="server"></asp:TextBox>
                                                </div>
                                            </div>
</div>
</div>
</div>

Thanks