How do I figure out a “DependencyProperty.UserValue” exception in my WPF/MVVM application?

I have a C#/.Net/WPF/MVVM application.

The application runs fine when running through VS 2015.

When I run the application standalone (on a different machine), I get the following exception at startup:


An unhandled exception of type "System.InvalidOperationException" occurred in WindowsBase.dll

Additional information "{DependencyProperty.UnserValue} is not a valid value for property "TopLevelItemTemplateKey"

What is really going on?

How do I debug this?

Thanks