WPF and Unity - No matching constructor found on type

In your App.xaml, make sure that you have gotten rid of the StartupUri="MainWindow.xaml" property being set. Since you have overriden the OnStartup of your application and provided a custom instance of the MainWindow you shouldn't be leaving the default StartupUri property being set in the App.xaml file and WPF desperately trying to instantiate a type without a default constructor.