that means that that file has been damaged.
and you can only hope that this is the only file that has been damaged, because it is one of the few files that contains no data.
make a new project and copy that new project's game.rpgproject file to your existing project.
if you get another error for another file after that, then more than one file has been destroyed and you need to replace them from your last backup.
and you need to find out why the files are destroyed to prevent future repeats.
where did you store the project? (full directory path please)
was there a computer crash before this?
Well.. I was going to post my randomly generated road experiments... But the new "Attach Files" on profile posts seems to be quite buggy. Also there's no more option to insert Imgur images. Highly unfortunate. Guess I'll give them a bit to fix it and go back to messing with stuff.