[Solved] Can't Group on a Column

[Alessandro]

Hi. I am binding a grid to a list of objects and I have the AutoGenerateColumns property set to true. However, I am also defining two columns in Xaml. The Xaml looks like this:

<telerik:RadGridView.Columns>
    <telerik:GridViewToggleRowDetailsColumn />
    <!--<telerik:GridViewCheckBoxColumn DataMemberBinding="{Binding Mode=TwoWay, Path=Tag.IsSelected, BindsDirectlyToSource=True}" Header="Selected" AutoSelectOnEdit="True" />-->
    <telerik:GridViewColumn Header="Selected"   >
        <telerik:GridViewColumn.CellTemplate>
            <DataTemplate>
                <CheckBox  IsChecked="{Binding Path=Tag.IsSelected, Mode=TwoWay}" Style="{StaticResource YellowCheckBoxStyle}" />
            </DataTemplate>
        </telerik:GridViewColumn.CellTemplate>
    </telerik:GridViewColumn>

    <telerik:GridViewDataColumn Header="Data source" DataMemberBinding="{Binding Tag.DataSourceName}" IsGroupable="True"  UniqueName="DataSourceName" />
</telerik:RadGridView.Columns>

The problem I have is that I cannot drag the columns defined in Xaml into the group box. Any ideas why I can't? Thanks for any help.
 -- xavier