Wpf Notifyicon is not displayed in Windows XP

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WPF

C#3.5

Hey,

I've got a huge problem with my code, while developing I just tested the program on Windows 7 and 10 systems.
Now the customer wants it to be used also on Windows XP machines, basically its written for .Net3.5, to be compatible with most systems.
On my Windows XP physical testmachine, I've got net 3.5 installed but my "taskbarnotifyicon", I'm using the popular library from hardcodet.net (V1.0.4.0 for .net 3.5), the icon is not visible. There is just a blank space, where it should be but no icon is displayed, even no mouseover-text and contextmenu is not available.
I debugged the program so far, that the problem is based on the icon.

Info Infofenster = new Info();
ContextMenu conMen = new ContextMenu();
MenuItem Info = new MenuItem();
public App()
{
   //other source, blabla
}
protected override void OnStartup(StartupEventArgs e)
{
        base.OnStartup(e);
        //some code, Database etc.
        Info.Click += OpenInfo;
        Info.Header = "Info";
        conMen.Items.Add(Info);
        icon = new TaskbarIcon();
        icon.Icon = AmpelStempelzeit.Properties.Resources.ledAnwesend;
        icon.ToolTipText = "Eingestempelt";
        icon.Visibility = Visibility.Visible;
        icon.TrayPopup = new Popup(icon);
        icon.ContextMenu = conMen;
}
protected override void OnExit(ExitEventArgs e)
{
        icon.Dispose();
        base.OnExit(e);
}

Running on Windows 7, 8, 10 works great, probably WinXp cant handle the "Resourcepath" for images?
I really have no idea.

Regards from snowy Germany,
Vince