I was having the exact same problem trying to sync my iPod.
After reading everyone's suggestions I decided to switch my iPod to manual file management (which I normally prefer anyway) and then created individual smart playlists under the condition "Artist Starts with (blank)" and went down the alphabet letter by letter.
I would then drag the playlist to my iPod and let it update.
When I got the error, I just browsed the smart playlist and dropped files onto the iPod in batches of about 50. Finally got the error message again and reduced the range to 10.
Turns out I had one file, Kill the King by Megadeth, that was locked. One file out of nearly 10,000 songs, videos and pictures. I just apple-clicked the file, clicked "open in finder" in the drop-menu and unlocked the file. Boom.
I was then able to sync my iPod like normal. (Actually, I just dragged my whole iTunes library to the iPod and let it upload the songs which were cut-off after the (-54) error.)
I also had a few DRM files my brother had downloaded to my hard disk using his iTunes account. I just deleted those.
Whole thing took about 15 minutes.