This can be do to a number of different reasons, and without more information it's hard to know just what happen. One possibility is a hardware failure of your storage card. I have seen cards that work until you fill them to a certain point. Once that point is reached, bang and files disappear. If only the media library is gone and everything else is okay one possibility is a sync failure. Did you perhaps have a sync fail or did you interrupt one? You might want to insert the card in a PC and scan it for errors with the PC. This can also be caused by trying to write to the card, with a low battery.
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David Hettel
Moderator
This can be do to a number of different reasons, and without more information it's hard to know just what happen. One possibility is a hardware failure of your storage card. I have seen cards that work until you fill them to a certain point. Once that point is reached, bang and files disappear. If only the media library is gone and everything else is okay one possibility is a sync failure. Did you perhaps have a sync fail or did you interrupt one? You might want to insert the card in a PC and scan it for errors with the PC. This can also be caused by trying to write to the card, with a low battery.