iPhone Music: When click song to play, I get 'resource unavailable'

on my iPhone, when I sync to my iTunes library on my computer, click song to play, I get ' resource unavailable' for all except a few songs, which work fine. Logged in and out if iTunes/App Store, reset computer and phone, no change. I am using my home network, not trying a cellular connection. Just started after last iPhone update a couple days ago.