I had a similar problem with my Wewa 256MB mp3 player. I deleted all the files on the disk but my computer still said it was full, so I formatted the drive. Then I got the error message: "Error! Reformat drive".
Right-click on the removable drive (your mp3 player) and choose 'format' and then under 'file system' choose FAT and do not select 'quick format'. This worked for me, and I was able to load files onto it and play mp3s again. Hope this helps.
Warren, September 2007