Calendar is showing behind the iframe in asp.net

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ASP.NET

Hi,

Am using calendar extendar to select the date. Based on date am showing the records in pdf using iframe. after showing the record if i click the date calendar is going behind the iframe. Only in IE7 and IE8 its not working. below IE7 its working.

Am have tried z index. but no use. Please can anyone solve my prob.

This is my code

<table cellpadding="0" cellspacing="0" border="0" width="100%" align="center">
    <tr>
        <td align="center" style="width: 100%; position: relative;">
            <div>
                <asp:Label ID="Label1" runat="server" CssClass="LabelStyle1" 
                           Font-Bold="False" Text="As of date"></asp:Label>
                <asp:TextBox ID="txtSrtDate" CssClass="TextBoxStyle1" 
                             onclick="javascript:return hi();"
                             runat="server" Width="100px"></asp:TextBox>
                <cc1:CalendarExtender EnableViewState="true" ID="dtDate" 
                                      TargetControlID="txtSrtDate"
                                      Format="dd/MM/yyyy" runat="server">
                </cc1:CalendarExtender>
                <asp:Button ID="btnShow" runat="server" CssClass="ButtonLoginPage"
                            Text="Show" ValidationGroup="DateValidation" />
            </div>
        </td>
    </tr>
    <tr>
        <td align="left">
            <div id="div2">
                <iframe runat="server" id="ifShowPdf" visible="false" width="100%" 
                        height="650px">
                </iframe>
            </div>
        </td>
    </tr>
</table>

Thank You

[Modified: just fixed the tabbing so it was more readable.]