@Alexandros >
When the message is shown, the reasons for this issue may be among the following 3 cases:
・No track file: Even though the user said "NOTHING with exclamation mark on front", only when a track is selected, an exclamation mark will be shown. The track may be missing when you select the track. Please select a track when this issue occurs.
・USB flash drive may lack in storage space → Please check the remaining space in the device.
・Failure of the USB device → Please try using other USB devices.