When i try to import a song on Itunes it comes up not available, can anyone help me?

I just bought a whole bunch of new cds, and for some reason when i try to import them half of the cds track comes up not available... I have had itunes for years and i keep it up to date so its not like i just downloaded it and im having this happen. Also i have plenty of hard drive space so that cant be the issue. Any help will be much appreciated. Thank you