Fix Bug：
About the error message, I suggest you try the following steps to add the reference to the project:
#1. Right click on your project
#2. Navigate to “Add” and click on “Reference…”
#3. Go to “Assemblies” and enter “Microsoft.Windows.Design.Extensibility” in the search box
#4. Check the “Microsoft.Windows.Design.Extensibility 4.0.0.0” checkbox and click on OK
#5. Re-build your project and check if the error disappears