Sorry you are having trouble. It seems the project file is corrupt. In fact, looking at it with a hex editor the file is all zeroes, so unfortunately there is no data there to recover.
Spine stores your project files periodically and just before you save, so you should be able to get your project file from your backup folder:
Settings - Spine User Guide: Backups
I don't know how this could have happened. It could possibly have been an error with the storage device, or the OS wasn't able to flush the data to disk, eg due to an OS crash or power loss. Something like that should be quite rare!
