Seadragon in TabPanel -- Image not shown

I have this code:

<ajaxToolkit:TabContainer
	ID="TabContainer1"
	runat="server"
	ActiveTabIndex="0"
	Height="2500px"
	Enabled="true"
	UseVerticalStripPlacement="true"><ajaxToolkit:TabPanel ID="TabPanel4" runat="server" HeaderText="Diagram"><ContentTemplate><div><ajaxToolkit:Seadragon id="sd" runat="server" Height="800" Width="800"
                                           SourceUrl="images/dzc_output.xml"></ajaxToolkit:Seadragon></div><br /><asp:ImageMap runat="server"
			ID="imageObject"
			BorderWidth="0"
			BackColor="#FFCCFF"
			ImageUrl="images/dashBoard/CS500.png"
			HotSpotMode ="Navigate"></asp:ImageMap></ContentTemplate></ajaxToolkit:TabPanel></ajaxToolkit:TabContainer>

The SeaDragon container is on the page on the TabPanel, but the image is not shown. When I move the SeaDragon container above the TabContainer, the image is shown. I used Deep Zoom Composer to make the SourceURL.

Can anyone help with getting the image shown?