I\'m running a .Net 4.5 WPF application in Visual Studio 2015 Update 1 in a Debug build configuration.
In Tools > Options > Debugging > General I have checked Enable UI
I had the same issue and resolved it by also selecting the "Preview selected elements in Live Visual Tree" sub-option (i.e. under Tools > Options > Debugging > General > Enable UI Debugging Toos for XAML). Whenever I unchecked that option, the Live Property Explorer and Live Visual Tree windows would go back to showing the "UI Debugging is either disabled..." message again.