If your card is not detected, or the content of the card is not detected.
1. Remove and reinsert the SD card into the device
2. Try to Format the SD card
Use a microSD card that has been formatted on the Walkman.
Sony does not garuantee the operation of other microSD cards.
Sony does not garunatee all operations for microSD cards that
are used on multiple devices.
3. Perform a factory reset of your device.
For more information about using microSD card, please read this FAQ
If the issue still persist your device might need repair. Please contact Sony Support.