After you posted the image, I see the image is in a different project. That's important to know.
- Make sure the
Build Action
for you image is set to "Resource". - Make sure the
Hotelverwaltung
project referencesFachlogik
.
Then try setting the location like this:
Icon="pack://application:,,,/Fachlogik;component/Images/icon.png"
You can't set a relative path like that to go between projects.