I think you experienced "grey" songs issue? I found this somewhere on this board:
So after a lot of messing around with iTunes on my mac and iPhone I finally got rid of them (ghost songs in iTunes that aren't showing on iPhone). Hopefully this will help other people too.
I followed the instructions in another thread and downloaded a program called PhoneView(the demo version worked fine, no need to pay).
Connect your iPhone to mac, open PhoneView, go to Settings>Show entire disk. Here I would recommend you back up all the contents of your phone.
Now this isn't my most technical piece of work but I went on a bit of a deleting spree (again make sure you've backed up everything).
I deleted the contents of the following folders:
Purchases,
Downloads,
iTunes Control>Sync>Media,
iTunes Control>Music
Then I deleted the following files from iTunes Control>iTunes:
MediaLibrary.sqlitedb
MediaLibrary.sqlitedb-shm
MediaLibrary.sqlitedb-wal
(and maybe a couple of others but these are the ones I remember).
I then reset the iPhone (Hold the Home and Power buttons for 5 secs), synced with iTunes and they had gone. Rejoice.