When I transfer some MP3 music files from my laptop to my Nokia 150, they become unusable once I unplug the USB. I used mp3 diags and mp3val on the transferred files. Mp3 val claimed the format is unknown (windows says it's still mp3), and mp3 diags said the files have no mpeg audio stream and no id3 tags. Indeed, there isnt even any visible info of length or bitrate. Somewhere I read of a simmilar case, where it was replied that the files are actually m4a or aac and that's why mp3 diags is confused. I tried conversion with apowersoft video converter studio, I got an error when selecting the files for conversion. Is there something else I can do? P.S.: it's definitely not the laptop nor the usb cable.