I've been getting a strange error pop-up for awhile now every time I back-up/sync to iTunes. At the end a pop-up comes up saying "Can't write to Macintosh HD unknown error -54" but it syncs apps and updates my palylists fine. It also makes a backup (it says backup was last created xxx) with no problem. Only other thing is the apply button appears as well though when I click it it goes away. BTW I make full encyrpted backups. Not sure what the issue is - I had this problem briefly on my old computer last month but it never seemed to affect anything either?