ipod suddenly stuck in read-only

Hey all, I have a newly refurbished iPod classic 5th gen that has suddenly gotten itself stuck in read-only mode. It worked fine for about a week, I copied all the music I wanted and made the playlists I wanted, but yesterday I started getting error messages. When I attach it to my computer, I get two errors: "Mac OS X cannot repair this disk. You can still open or copy files on the disk, but you can't save changes to files on the disk. Please back up and reformat the disk as soon as you can.", and from iTunes, "The ipod ... could not be synced. You do not have the privilege to make changes." I get a similar error when I try to copy additional files to the ipod. "Attempting to copy to the disk ... failed. You do not have the privilege to make changes."

Here's what I've tried. I thought it looked like a permissions problem. When I bring up the info from the finder to look at the permissions, it says "You only have permission to read," BUT in the box below says my user has read and write permission, and staff and everyone has read only permission. I can click the lock to make changes, and I can check or uncheck the box to ignore ownership, and that will change the heading from my username to system, still showing read and write permissions, but, I can't change the permissions there even after unlocking.

I tried repair permissions through terminal, and got this:

sudo diskutil repairPermissions /Volumes/my_ipod

Error starting permissions repair for disk1s3 my_ipod: Unable to determine the Mac OS X version on the targeted disk (-69831)

and repair volume:

sudo diskutil repairVolume /Volumes/my_ipod

Started file system repair on disk1s3 my_ipod

Error: -69888: Couldn't unmount disk

Manually changing the permissions:

sudo chmod -r 755 /Volumes/my_ipod

chmod: Unable to change file mode on ...: Read-only file system

When I look at it with ls, permissions in terminal for the ipod are shown as "drwxr-xr-x@". I am running OS X 10.8.4.

This is getting frustrating. Why would this have happened in the first place? It was fine yesterday morning, and then this started happening seemingly without any warning when I tried to add some more songs after work. I'd really rather not have to format and restore. How else can I approach this?