First: Have you checked the card to see if there's enough room to save additional files?
Second: Have you tried another card? Sometimes bad cards happen.
Third: Have you tried removing the card and RE-SEATING it? Unless the card is fully seated in the slot it may not function correctly.
Fourth: Do you have TMC installed? If so, does it function as intended - ie - display files, perform backups to the [PC/Mac], display time code, etc etc etc?
CaptDan