You somehow tried to link the SiteMapDataSource back to itself:
Code:
<asp:SiteMapDataSource ID="SiteMapDataSource1" runat="server"
SiteMapProvider="SiteMapDataSource1" />
The bold part shouldn't be there. In the book, the code looks like this:
Code:
<asp:SiteMapDataSource ID="SiteMapDataSource1" runat="server"
ShowStartingNode="False" />
Hope this helps,
Imar