OK, so the text is accurate. That's good.
Why not make saving work how it does in most games (including autosave-only games), where starting over doesn't disable save functionality until the game relaunches? The way it is now seems like lost progress waiting to happen.
Or, if this would be much easier, why not put a large warning box up when the player is in this no-save state? SAVING DISABLED / CLOSE AND REOPEN GAME, something like that.