John, you’ve attached the MusicXML file, not the Dorico project itself: unfortunately I can’t diagnose any problems with your Dorico project from the MusicXML file you used to create the Dorico project. Certainly your MusicXML file imports OK into Dorico for me, and I’m both able to save and re-load the resulting Dorico project file.
I suspect whatever problem you’re having is caused by the layout options problem discussed earlier in the thread, and if you both delete the layoutOptions_*.xml files from your user data folder and manually re-link the necessary flows/players to layouts in your troublesome project, all will be well.