Why can't some songs on my iTunes be played?

I just uploaded a CD onto my iMac, and it played perfectly fine on it. However when I synced my iPhone to it and disconnected it after the sync, I couldn't play it on my iPhone? Like the songs were there, but the color of the titles were a light grey. Please advise!

Don't worry this happened to me before. Basiclly your iTunes sync on your iPhone has gone just a little wrong! When they are still in grey on the music app, it means the songs haven't successfully gone across. All you need to do to resolve this is; Plug your iPhone into your PC and load up iTunes. Then sync the iPhone whilst syncing go to music which is your music library at the top left. After that select the songs that are in grey on the iPhone and drag them across to where it'll say ---'s iPhone then let them go after the ---'s iPhone bit has turned blue. Then on the iPhone go on the music app and locate the songs. They should be in grey but with a little blue circle going round. Then they will be black and ready to play when sucessfuly on the iPhone. Be patient and wait til sync is over and if still not done keep trying! It's what I did and I got there!

They probably are not the right format. Your computer does not recognize the file.

If you're trying to play a song on a CD or DVD that you burned in iTunes, make sure that the equipment you're trying to play the CD or DVD on is appropriate for the disc's format. For example, if you burned an audio CD on a CD-RW disc, you can only play it in your computer. If you burned an MP3 disc, it should play in your computer and in special MP3 CD players, but not in standard consumer audio CD players.