Well, this is a new one, and right now I’m stumped. I’m guessing that the build runs on to generate “MakePri: error 0x80080204: Appx manifest not found or is invalid.” and then terminates shortly after? Returning to focus on the xml content itself and the validation process: can you see anything at all in the xml file that would be throwing off the parsing (sneaky unrenderable characters etc.)? Also, do you know what version of the Win10 SDK you have installed (since that’s where the schema comes from)?