Remove StartingNodeOffset="1" , you should not specify that on any sitemapdatasource, you can specify it on a menu but you should not specify it on the data source.

maybe you are editing the wrong file. When I add that it causes the problem you describe and when I remove it it fixes the problem.

I would look in the log and see if any clues are logged.

Also I can tell that you produced your own build from source code in between releases, maybe get the latest code or use an official release. I just made a new release today.

If you modified the source code then possibly it created a problem.

SiteMenu does not affect the sitemap at all. It is fine to set the menu properties however you like but you should not set startingnodeoffset on the SiteMapDataSource because the same data source is shared by the sitemap and the SiteMenu

In my first answer to you I said to change it on SiteMapDataSource because you posted this:

<asp:SiteMapDataSource ID="SiteMapData" runat="server" ShowStartingNode="false" StartingNodeOffset="1" />
<asp:SiteMapDataSource ID="level3datasource" runat="server" ShowStartingNode="false" StartingNodeOffset="2" />

and it is not correct, you should change it to this:

<asp:SiteMapDataSource ID="SiteMapData" runat="server" ShowStartingNode="false" />
<asp:SiteMapDataSource ID="level3datasource" runat="server" ShowStartingNode="false" />

you can do whatever settings work for you on <portal:SiteMenu

Please explain what you are trying to accomplish by using that setting on the site menu. It may be that the menu actually sets the property on the datasource and then when the sitemap tries to use the same datasource it causes this problem.

Normally that setting is useful on on PageMenu which is designed to be a sub menu but on the main menu (SiteMenu) you would typically show top level pages and not need this setting.