Why does the message MG ERROR appear in the display?

MG ERROR appears in the display and the Network Walkman cannot playback the audio file.

This message appears when there is a problem with all or a part of the data stored in the built-in flash memory/Memory Stick.
Please follow the steps below to erase audio data that cannot be played back.

1. Connect the Network Walkman to the computer and transfer all the audio files and data to the computer.
2. Disconnect  the Network Walkman from the computer and format the built-in flash memory/Memory Stick using the FORMAT function on the Network Walkman.