Hi, after alot of hassle, I have sussed it.
When you download files from media player , I was copying the songs into the MICIN.DIR file. ( the system seem to do this automatically)
To make sure you can play the songs, I then copied and pasted the song icons into the F:/ (this drive is the USB port directly linked to the MP3 Player- this may be a different drive on your computers( but it is the device drive) directly avoiding the MICIN.DIR file and the songs are there and play successfully.
Have not sussed how to do this from AAC files yet though. Hope this helps all of you having the same trouble as me.
Susan Braby, October 2006