It's trying to write to the save folder and can't, which usually means Windows user access control is preventing it, but running as admin would've corrected that. Just to rule out the other obvious cause, check to see if you're really low on disk space on that drive.
If that's not it, go to the start screen, click on troubleshooting, and then Enable debug trace. Exit and re-start the game, then exit again, and a text file should pop up (if it doesn't, you can find it in the \debug folder.) Post the contents of that file in a message and it may give us a better idea of exactly what is going wrong.
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