If your save won't load, it's likely corrupted. You can't fix that. Load an earlier save, if you have one.
It's the usual things:
- Don't switch off or reset your PC while the game is saving and give FM 30 seconds to a minute after saving before resetting or switching off.
- An anti-virus could have also corrupted it, so put the FM folders and the temp folders in the exceptions list.
- Run a 3/5/10 file rolling save so you always have a backup save.