Welcome to Android Central! The card is likely corrupt or counterfeit. Counterfeit cards are relatively common--they take a small capacity card and reprogram it to think it's larger capacity. But once you try to save data to the card beyond its capacity, some or all of the files can get corrupted or lost. Use
SD Insight to see if your card is valid. If it is valid, then unmount the card (in
Settings>Storage), remove it, and insert it into your computer. Then run chkdsk to look for bad sectors:
http://forums.androidcentral.com/am...guide-using-chkdsk-fix-corrupted-sd-card.html.
Hopefully, you didn't use the Move function to transfer those photos to the SD card, because Move deletes the source files once the operation is complete. Copy is always a better function to use, because if something messes up in the file transfer, you still have the original file.