Ok so I'm home from the desert & free from the sub-dial up internet speed over there, & have been buying songs of of iTunes like there's no tomorrow (actually, I only have 28 more tomorrows before I head back). I got the pop up windo asking me do I want to back up purchases, so I say yes, insert an archival quality DVD , & back up, no problem, I think. About 2 hours & 4 more album purchases, I get asked again to back up, so I reinsert the same dvd, & I get the message "insert blank DVD" . I chose only to back up what has changed, & the info at the bottom of the screen when I click "Purchases" says I've only downloaded 3.63 GB, so I know the dvd is not full. Did I miss a step, like having to format the DVD or something? I should be able to continue to use the same dvd until its full, right? TIA.