I'm playing a single player game with simultaneous turns. I'm about 150 turns in and wanted to try reloading 1 turn back to undo a boneheaded mistake. So I loaded the last autosave, took my turn, and hit end turn.

As processing started it gave an error "unable to load empire" and then continued to process. When it finished processing all of the orders I had given, and ships I had created, had been undone.

What can I do to get around this error? Is my game now unplayable? Is it not possible to go back to an earlier save in a simultaneous game?