There is a Lock switch on the left side of the SD card. Make sure the Lock switch is slid up (unlock position). You will not be able to modify or delete the contents on the memory card if it is locked.
NOTE: If you are using a microSD/microSDHC card or a miniSD/miniSDHC card, insert the card into the standard SD adapter.
From Sandisk - Toggle the lock switch.
If the lock switch is not on lock:
1. Slide the switch up and down. Repeat this 3 times.
2. Let it stay on the Lock position for 30 seconds.
3. Slide the switch up to unlock the card.
4. Try to transfer files into the device.