"Cannot set Name attribute value 'Label1' on element 'Label'. 'Label' is under" & _
  "the scope of element 'MyTabItem', which already had a name registered when" & _
  "it was defined in another scope. Zeile 71 Position 61."

<TabItem x:Class="MyTabItem"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" >
    <TabItem.Resources>
        <DataTemplate x:Key="RemoveButtonTemplate" >
            <Grid x:Name="Grid1">
                <ContentPresenter ContentSource="{Binding}" Content="{Binding}" _
                  Margin="0,0,22,0" />
                <Button Name="btnRemove" Template="{StaticResource" & _
                "RemoveButton}" Width="15" Height="15" _
                HorizontalAlignment="Right" VerticalAlignment="Center" />
            </Grid>
        </DataTemplate>
 
        <DataTemplate x:Key="DefaultTemplate" >
            <ContentPresenter ContentSource="{Binding}" Content="{Binding}" _
              ></ContentPresenter>
        </DataTemplate>
 
    </TabItem.Resources>
</TabItem>