AJAX Calendar control

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I have a TextBox with a calendar control like this. But, when I click on the
image, it just posts without showing the calendar. However, when I place the
cursor in the TextBox, it shows the calendar. Why isn't my ImageButton
working?

<td align="left">
<asp:TextBox ID="txtEntryDate" runat="server" /<asp:ImageButton
runat="Server" ID="ImageButton3" ImageUrl="~\Image\Calendar.png"
AlternateText="Click to show calendar" />
<ajaxToolkit:CalendarExtender ID="ajaxCalendar2" runat="server"
TargetControlID="txtEntryDate" PopupButtonID="Image2" />
</td>
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Be Cool!