How to get All my songs to sync to my iphone?

I just bought an iPhone 4 and I noticed that a nice chunk of my songs weren't syncing from iTunes, they just turned grey with a syncing symbol next to them. I have the manually add song box checked, I have enough memory I've tried removing some songs and I can't figure out why they won't add. Any suggestions?

Try dragging the whole "Music" category in iTunes to your iPod. Also make sure you are authorized for those songs to be synced.

Update the song library properly then it will sync