<cc1:ModalPopupExtender BackgroundCssClass="modal"
                        DropShadow="true"
                        runat="server"
                        CancelControlID="btnClose"
                        PopupControlID="AddPanel"
                        id="ModalPopupExtender1"
                        TargetControlID="AddDatabase"/>


 <asp:Panel ID="AddPanel" runat="server" Width="500" Height="200"
                style="display:none;" >

 <div>
                    <asp:TextBox ID="txtUserName" runat="server" TabIndex="4"></asp:TextBox>
                <asp:RequiredFieldValidator ID="rfvUserName" runat="server" ControlToValidate="txtUserName"
                    ErrorMessage="*" Display="Dynamic"></asp:RequiredFieldValidator>
                    <asp:RegularExpressionValidator ID="revUserName" runat="server"
                        ControlToValidate="txtUserName" Display="Dynamic"
                        ErrorMessage="Enter Correct User Name"
                        ValidationExpression="^[a-zA-Z  .]{1,100}$"></asp:RegularExpressionValidator>
                </div>
</asp:Panel>