MuseScore saves out invalid MUSICXMl file
Open my file The Birth of the Blues. Export the piano part as MusicXML.
Close file. Open the exported MusicXML file.
Result: File 'File 'C:/Users/david/Google Drive/MusicXml/The_Birth_of_the_Blues.musicxml' is not a valid MusicXML file. Do you want to open this file anyway.
Note. If you open anyway, it seems to display ok. However, it crashes the app I was trying to export it to.