A small minority of people have had issues with loading or saving games on their devices.
In some cases this can happen if the device is unplugged without unmounting (ejecting) it first, because the card isn't firmly mounted in the device or 'just because' (the 'just because' normally happens on cheaper memory cards).
The link below explains how you might be able to repair such corruption:
Other possible causes of loading issues with save games:
* If the battery runs to a critical level the OS will request an autosave however on some devices the battery power will fail before the save is completed this will leave a corrupted save game on your device, you should however be able to load up all other save games which are present (including the previous auto-save).
* If you forcibly power down your device (ie. power off by holding down the power button etc.) then the OS will request a save but again might not allocate enough time for this to fully complete, again this should only affect a single auto-save slot and leave all others accessible.
It is heartily suggested that you never allow the device to fully power off while the game is active ...