ActiveX control (XMetal XMax) in AvalonDock generates error message

Question

I have an ActiveX control, which is an XML Editor (XMetal XMax). I have included this as a COM component (WindowsFormsHost) in my WPF project. The editor's content model, such as XML Schema, CSS, XML elements, XML attributes, etc., are pre-configured by an XMetal Developer utility, and assigned to the XML editor in the WPF implementation as a single file with the suffix ".xac".

Step 1 - Works: When I add the XML Editor to a grid (this.grid1.Children.Add (host)), everything works great. The XML Editor and all XML content is displayed.

Now I go one step further and have integrated XCeed AvalonDock as a layout base.

Step 2 - Does Not Work: The prerequisites are the same as in step 1. If I assign the XML Editor to the "x: Name" property of an "xcad: LayoutDocument", I get an error message. Although the symbol of the XML Editor is visible in the "xcad: LayoutDocument", the XML basic configuration .xac file will not be loaded. An error message appears.

As I said, when assigning to a Grid.Row everything works fine. I have tried a lot, but unfortunately without success. Can someone give me some help please. Many Thanks.

public partial class MainWindow : Window
{
    public AxXMetaLControlLib.AxXMetaLControl axXmax;
    System.Windows.Forms.Integration.WindowsFormsHost host;

    public MainWindow()
    {
        InitializeComponent();
    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        // Create the interop host control.
        host = new System.Windows.Forms.Integration.WindowsFormsHost();

        // Create the ActiveX control.
        axXmax = new AxXMetaLControlLib.AxXMetaLControl();

        // Assign the ActiveX control as the host control's child.
        host.Child = axXmax;

        // Add the interop host control to the Grid
        // control's collection of child controls.
        this.XMaxControl.Content = host;
        //this.grid1.Children.Add(host);

        // Load an XML File into XMAX
        axXmax.LoadFromFile("C:/Users/Administrator/Desktop/VS_XMax_PiMod/XMax_PiMod_01/instance1.xml", "C:/001_Mein/001_CMS_Projekt/01_Mein_Projekt/01_Finale/wCMS_02/XMax_Dateien/pi-mod.xac", XMetaLControlLib.SQDocViewType.sqViewTagsOn);

    }
}


<Grid x:Name="grid1">
    <StackPanel>
        <xcad:DockingManager>
            <xcad:LayoutRoot>
                <xcad:LayoutPanel Orientation="Vertical">
                    <xcad:LayoutPanel Orientation="Horizontal"
                      DockHeight="*">
                        <xcad:LayoutAnchorablePaneGroup DockWidth="150"
                                        Orientation="Vertical">
                            <xcad:LayoutAnchorablePane DockHeight="100">
                                <xcad:LayoutAnchorable x:Name="myXmax" Title="Tool 1">

                                </xcad:LayoutAnchorable>
                            </xcad:LayoutAnchorablePane>
                            <xcad:LayoutAnchorablePane DockHeight="70">
                                <xcad:LayoutAnchorable Title="Tool 2">
                                    <TextBox />
                                </xcad:LayoutAnchorable>
                            </xcad:LayoutAnchorablePane>
                        </xcad:LayoutAnchorablePaneGroup>
                        <xcad:LayoutDocumentPaneGroup>
                            <xcad:LayoutDocumentPane>
                                <xcad:LayoutDocument x:Name="XMaxControl" Title="Doc1">

                                </xcad:LayoutDocument>
                                <xcad:LayoutDocument Title="Doc2">
                                    <TextBox />
                                </xcad:LayoutDocument>
                            </xcad:LayoutDocumentPane>
                        </xcad:LayoutDocumentPaneGroup>
                        <xcad:LayoutAnchorablePaneGroup DockWidth="250"
                                        Orientation="Vertical">
                            <xcad:LayoutAnchorablePane>
                                <xcad:LayoutAnchorable Title="Attribute Manager">
                                    <xctk:PropertyGrid x:Name="propertyGrid" SelectedObject="{Binding}" >

                                    </xctk:PropertyGrid>
                                </xcad:LayoutAnchorable>
                            </xcad:LayoutAnchorablePane>
                        </xcad:LayoutAnchorablePaneGroup>
                    </xcad:LayoutPanel>
                    <xcad:LayoutAnchorablePaneGroup DockHeight="150">
                        <xcad:LayoutAnchorablePane>
                            <xcad:LayoutAnchorable x:Name="prop" Title="Tool 4">

                            </xcad:LayoutAnchorable>
                        </xcad:LayoutAnchorablePane>
                    </xcad:LayoutAnchorablePaneGroup>
                </xcad:LayoutPanel>
            </xcad:LayoutRoot>
        </xcad:DockingManager>
    </StackPanel>
</Grid>