1) Try replacing the project (.rvproj2) file. Tried that on your game, didn't helped - corrupted files.
2) If not... Well your data is corrupted - you can try replacing files in Data folder with new ones (or from backup), perhaps you'll find the corrupted one. Most of them (if not every single one) are corrupted.
3) If not... Use your backup.
4) If not... Well... Most likely you need to start a new project. Consider using backup-making script to prevent from losing data again.