I changed the album art and song/album/artist names on some songs and now they won't transfer. How can I fix this?

Within iTunes I added album art and changed the song/artist/album name on some songs. This was all done in iTunes, clicking on the names to edit them, right-clicking and using iTunes' 'Get Album Artwork' option to get artwork and all that jazz, so I don't understand why my Apple products seem to be having so much trouble with their own software. Anyway, when I try to sync my iPhone the songs that have been edited only show up as greyed out on my device and during syncing I get the error message that the files "could not be read or written". They all show up and play fine on iTunes, they just won't transfer. In addition those songs that I added album art to that DO transfer do not display the album art on the iPhone.