I agree this is not a useful error message. I am reaching out to our XAML folks to get an update on what investments we are doing to make debugging XAML issues easier and how we can share these with the community. We are planning to do a more dedicated On .NET session about XAML & Fluent in UWP, so hopefully we can address these topics there as well. Thanks for the feedback!
@pnp0a033: The manifest extensions that we have shown in the session are not available in the current Creators Update. If you are in the Windows Insider program you will start seeing some of them become available for you to test in the next couple of weeks. Once they are in an insider build we will publish samples on GitHub to help you get started. If you want to keep in touch on this topic, follow me on Twitter (@StefanWickDev) to see timely updates when things become available publicly.
We are not asking developers to abandon their WPF or other existing investments. In fact with the Desktop Bridge project we are enabling them to take advantage of the full power of Windows 10 with their existing code investments. They can keep their current code running without restrictions, packaged as a Universal Windows app package, and gradually take advantage of new UWP features at their own pace. They do get the best of both worlds.
Microsoft apps are taking the same path: some go straight to pure UWP (like OneNote or Paint), while others are doing the Desktop Bridge migration (like the full desktop versions of Word, Excel, Powerpoint).
As we have stated in the BUILD2017 session, we know that UWP is not complete yet, we have gaps to plug in order to support certain types of applications. We are making big steps forward in the Fall Creators Update by aligning with NET Standard 2.0 and by adding support for more Win32 APIs as well. There is more work happening beyond that and I would like to invite everyone to help with the prioritization by posting/voting on UserVoice:
To use this with the Visual Studio extension for debugging Desktop Bridge apps, create a new "Desktop to UWP Packaging" project in your solution and add the 'CentennialPackage' folder from the sample as your Package Layout.
Let me know if you have more questions about this.
@Jonny Yu: the Desktop Bridge can handle complex installers (MSI and other types of installers). Please be sure to read this topic which lists a number of caveats you should be aware of before starting your conversion: