This procedure will fix Error -48
First: Select your iTunes Playlists that you use to synchronise to your iPod.
Select View > "Find duplicates"
Now remove all duplicate tracks (files) from the iTunes Playlist(s) you have chosen to sync with your iPod. The playlist(s) must contain no duplicate tracks. (Don't delete files with the same name but by a different artist or on a different CD...these are not duplicate files, just different versions of the same song, etc.)
When you are confident that no two tracks are the same click on the iPod icon in iTunes and select the "Summary" tab and press "Restore". This will wipe the iPod, update the software to 1.2.1 (if it's needed) and copy your new Playlist(s) with no duplicate tracks over to the iPod.
THE TRICK IS TO MAKE CERTAIN YOUR iTUNES PLAYLIST HAS NO TRUE DUPLICATE TRACKS BEFORE COPYING TO THE iPOD.
For some reason when you drag tracks to add to your Playlist in iTunes they sometimes get duplicated...I don't know why this happens but it is what causes the directory errors on your iPod. Checking you have no duplicate files in your iTunes playlists before syncing to your iPod will prevent this error from occurring.
Many different Macs since 1984, Mac OS X (10.4.7), I have one XP PC for playing games...but the OS is rubbish & the games too buggy