I've had this myself on a few occasions, more so the last FM. I could not find a way of loading it so unfortunately I lost the save completely. Going forward though I changed the preferences to have 3 rolling saves, this way if the problem occurs again i can at least go to the 2nd latest saved game. You do go back to whenever the last time the game was saved, but it's better than losing it altogether. I have the settings to autosave each month. Hope you fix it!