probably a bad sd card, there are tones of info regarding sd cards on the 708. just type sd or sd card on the search bar above and you will find everything about it. good luck.

 Did you format the SD card before you inserted in.............? if not than worth trying it.............

 Hi, please help to check if the SD card has been locked when you insert it. Or you may format the SD card and download all update again if your device is still within update period. Or change another new SD card to check the result. If there is still problem, then there may be problem with the card slot and that needs to return for repairing. Please try and good luck!