When I'm transferring songs to my Zen, there's generally no problem but some songs give an error that they can't transfer yet there's no problem playing them within amarok.  Any ideas what the problem is? Thanks.

Could the file type be not supported by your Zen? In this case, you want to install transkode (find it on kde-apps.org) which will convert a song automatically to a format your player understands.

No, all my files are mp3 format.

I get this from time to time and it's always been down to the paths where the MP3 files are stored. If there's a none-ASCII character anywhere in the path (or filename) it gives that message.