Just a heads up, if you switch between playing this game offline and then online your save file will be destroyed. The game will say your save is outdated or inaccurate. After that you can still cancel the load operation but it will already be too late. How they missed something so simple is beyond me.
I don't think switching between playing online and offline is the cause of this corruption. If it is, it certainly isn't the ONLY cause, as I have been online the entire time I've been playing and have run into the same issue. Does anyone know of any workarounds or if Cave is working on a patch?
I have the same problem, but it doesn't happen all the time and I don't get the "corrupt" message. It's just that sometimes, I start the game and it doesn't detect any save file so it creates a new one. And I think I have always played on-line.
I managed to finish the game and get all achievements but the the time ones in worlds 4 and 5, but since then the saved games has been erased twice. I'm not playing again until it is fixed.