Cant hear some songs in iPod

[AJelovac]

Hello just today i dowloaded spotify in my ipod touch. I sync some of the playlist to have it in offline mode. But some of the songs doasnt appear and it says to me is not possible te hear it (offline and online, just dont let me hear it). Sorry for  my english, the exact message i recive is Tema no disponible (in english is something like song not allowed)