Music not syncing on ipad

[hampshirelad]

Hi, some of my music syncs from my PC to my ipad but other tracks are greyed out, I have the PC and ipad on the same wireless connection and both spotify apps open. Some music is syncing but others not, all are ticked available offline on the ipad, for instance Linking Park sync'd ok but the Enermy will not. Can anyone help, there does not appear to be that much help for ipad but mainly ipod or phone. I am on a trial at the moment and thought that Spotify would solve all my problems that I have with Sonos and itunes but at the moment I would be reluctant to pay for a full service. Thanks for any advice