Suddenly cannot listen to music without wifi?

I like having access to my complete library at all times so I have a 32GB itouch. The other day I downloaded a new song so I connected my iPod to my laptop to get the song on the device (the Wi-Fi in my apartment is spotty so connecting with an actual cable works best.) All of a sudden all of my music is unplayable. I either get an "item not available" or a "connect to Wi-Fi" message. Itunes recently updated, but I have never had this problem in the past? Now all of my music is unplayable and I'm beyond frustrated. I've tried restoring it multiple times and nothing has worked. Please help, I'm desperate at this point.