F107 flashing LED meaning during playback

[amc252]

Hello everybody,
I just bought a Roland F107 digital piano.
I followed the manual instructions to play back either audio and MIDI files from a USB memory, but nothing happens.
What i get istead are the volume LED flashing in a pattern like this:
*
°
*
°
*
I couldn't find any explanation in the manual. I also contacted Roland customer service but got no answer yet.
Can anyone explain to me what these three flashing LED mean?

PS I formatted the USB memory to FAT32, renamed both the audio and MIDI files in different ways as suggested elsewhere but to no effect.

 

[amc252]

Eventually, I got an answer from Roland customer service.
It means the audio file one's trying to play is an a format different from 16bit 44100 hz.