some of the items could not be copied because they cannot be played on this iphone - however these tracks have played fine for months? Help!

Hi all,

I put a new album on my itunes this morning and synced with my iphone 5s, no problems. I also added a couple of other tracks that were floating about in my Music folder. They synced successfully. I then synced again, and all of a sudden i get the error message saying "some of the items could not be copied because they cannot be played on this iphone". it listed the items, all of which are albums that have been on my phone for months and played without issue. I haven't edited or moved these files at all. I have tried re-syncing several times, I have restarted itunes and tried again, and I have uninstalled and re-installed itunes with no joy.

Any ideas?