关于点击按钮弹出日历框的问题

我使用下面的代码：<div id="LayerC1" style="left: 173px; width: 189px; position: absolute; top: 66px;
                height: 191px; background-color: white" visible="false" runat="server">
                <asp:Calendar ID="Calendar1" runat="server" BackColor="White" BorderColor="#3366CC"
                    BorderWidth="1px" CellPadding="1" DayNameFormat="Shortest" Font-Names="Verdana"
                    Font-Size="8pt" ForeColor="#003399" Height="200px" Width="220px" OnSelectionChanged="Calendar1_SelectionChanged">
                    <SelectedDayStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
                    <TodayDayStyle BackColor="#99CCCC" ForeColor="White" />
                    <SelectorStyle BackColor="#99CCCC" ForeColor="#336666" />
                    <WeekendDayStyle BackColor="#CCCCFF" />
                    <OtherMonthDayStyle ForeColor="#999999" />
                    <NextPrevStyle Font-Size="8pt" ForeColor="#CCCCFF" />
                    <DayHeaderStyle BackColor="#99CCCC" ForeColor="#336666" Height="1px" />
                    <TitleStyle BackColor="#003399" BorderColor="#3366CC" BorderWidth="1px" Font-Bold="True"
                        Font-Size="10pt" ForeColor="#CCCCFF" Height="25px" />
                </asp:Calendar>
        </div><div id="LayerC2" style="left: 173px; width: 189px; position: absolute; top: 66px;
                height: 191px; background-color: white" visible="false" runat="server">
                <asp:Calendar ID="Calendar2" runat="server" BackColor="White" BorderColor="#3366CC"
                    BorderWidth="1px" CellPadding="1" DayNameFormat="Shortest" Font-Names="Verdana"
                    Font-Size="8pt" ForeColor="#003399" Height="200px" Width="220px" OnSelectionChanged="Calendar1_SelectionChanged">
                    <SelectedDayStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
                    <TodayDayStyle BackColor="#99CCCC" ForeColor="White" />
                    <SelectorStyle BackColor="#99CCCC" ForeColor="#336666" />
                    <WeekendDayStyle BackColor="#CCCCFF" />
                    <OtherMonthDayStyle ForeColor="#999999" />
                    <NextPrevStyle Font-Size="8pt" ForeColor="#CCCCFF" />
                    <DayHeaderStyle BackColor="#99CCCC" ForeColor="#336666" Height="1px" />
                    <TitleStyle BackColor="#003399" BorderColor="#3366CC" BorderWidth="1px" Font-Bold="True"
                        Font-Size="10pt" ForeColor="#CCCCFF" Height="25px" />
                </asp:Calendar>
        </div>
后台代码：   protected void Calendar1_SelectionChanged(object sender, EventArgs e)
    {
        starttime.Text = Calendar1.SelectedDate.ToString();
        LayerC1.Visible = false;
    }   protected void Calendar2_SelectionChanged(object sender, EventArgs e)
    {
        endtime.Text = Calendar2.SelectedDate.ToString();
        LayerC2.Visible = false;
    }
我有两个选择按钮，点击分别可以选择开始时间和结束时间显示到text中，但是我用相同的方法换了名字以后第二个日历层可以弹出来但是选择日期的功能无法实现，求解