<cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" BehaviorID="popup" TargetControlID="cmdTrigger"
            PopupControlID="pnlPopup" BackgroundCssClass="modalBackground"
            OkControlID="btnOk" >
    </cc1:ModalPopupExtender>
    <asp:Panel ID="pnlPopup" runat="server" CssClass="modalpopup" Style="display: none">
        <div class="container">
            <div class="header">
                <asp:Label ID="Label1" runat="server" CssClass="msg" Text="Add a new Entry" />
                <asp:LinkButton ID="LinkButton1" runat="server" CssClass="close" OnClientClick="$find('popup').hide(); return false;" />
            </div>
            <div class="body">
                <asp:Label ID="Label2" runat="server" CssClass="msg" Text="Name" />
                <asp:TextBox ID="txtName" runat="server" Width="346px"></asp:TextBox>
                </div>
            <div class="footer">
                <asp:Button ID="btnOk" runat="server" Text="Save" Width="48px"   />
                <asp:Button ID="btnCancel" runat="server" Text="Cancel" Width="50px" OnClientClick="$find('popup').hide(); return false;" />
            </div>
        </div>
    </asp:Panel>

<asp:Button ID="btnCancel" runat="server" Text="Cancel" Width="50px"
   OnClientClick="$find('txtName').value = '';
                  $find('popup').hide();
                  return false;" />