i have a new refurb macbook air 11 i just got recently,and everytime i try to buy music in itunes,it says something about write permissions or changing permissions in the itunes media folder,i went and checked all that and it says read and write under the permissions,i tried deauthorizing it won't let me gives me the same error,i even tried deleting and reinstalling itunes,i really need some step by step help on how to fix this it would be greatly appreciated.Thanks