Hast du schonmal versucht, das TabPanel in den TabContainer reinzutun?
Also so (ähnlich):
Code:
<ajaxToolkit:TabContainer runat="server"
OnClientActiveTabChanged="ClientFunction"
Height="150px">
<ajaxToolkit:TabPanel runat="server"
HeaderText="Signature and Bio"
<ContentTemplate>
...
</ContentTemplate>
/>
</ajaxToolkit:TabContainer>