I just dug this out of the archives, it was originally published on my old website lawsie.com (now defunct) many years ago.
oRite make a really great mp3 player called a music cookie, the model I have is the MU-280 and it's great! However I was adding the tracks on the mp3 player once and all appeared well and I could see the files using windows explorer but when I tried to listen to them I just got the message NO FILE EXIST. When I plugged the mp3 player back into my computer I could still view the files, what was going on?
No File Exist - The ANSWER
On the bottom of the music cookie there are three buttons, from left to right they are Vol- MENU & Vol+ Press the menu button then use the volume button to scroll down to 'setting' then click the menu button again. Using the volume buttons again scroll down to 'Erase' and click the menu button again. Scroll down to 'Format' and hit the Menu button again. You will lose the songs you have on the music cookie but this will restore the Music Cookie file structure (that's just my guess) and when you load it up with mp3s again everything will be back to normal.