C# - Tab Control Causes Index Out Of Bounds Error On Callback?

I have a simple application with a GridView bound to a LinqDataSource and a DetailView that displays a row from the GridView when it's selected. This works as expected. But now I'm placing the GridView and DetailView in separate TabPanels in an asp.net ajax Tab Control.

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</asp:ToolkitScriptManager>
<asp:TabContainer ID="CourseFinder" runat="server" ActiveTabIndex="0">
<asp:TabPanel ID="ResultsTab" runat="server" HeaderText="Results" >
</asp:TabPanel>
<asp:TabPanel ID="DetailTab" runat="server" HeaderText="Detail">
</asp:TabPanel>
</asp:TabContainer>

and my code behind file

protected void Page_Load(object sender, EventArgs e)
{
CourseFinder.Tabs[0].Controls.Add(Results);
CourseFinder.Tabs[1].Controls.Add(DetailsView1);
}

When I run the page I'm getting

[ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index]
System.Collections.ArrayList.get_Item(Int32 index) +7483656
System.Web.UI.WebControls.GridViewRowCollection.get_Item(Int32 index) +13
_Default.Results_SelectedIndexChanged(Object sender, EventArgs e) in c:Documents and
SettingsAdministratorMy DocumentsVisual Studio
2008WebSitesWebSite1Default.aspx.cs:35

The line of code getting the error is the one attempting to get the SelectedIndex from the GridView and update my DetailView.
GridViewRow row = Results.Rows[Results.SelectedIndex]; I stepped through the code with the debugger and SelectedIndex is not negative and it's not larger than the number of rows in the GridView. So I'm confused why simply placing the controls inside a Tab is causing this error?