I have been having trouble backing up to a DL DVD. When I input the disc, it says "this is not a blank disc" and spits it out. I got around it once by letting the dialogue in the finder pop up and selected "open in itunes" and then clicked backed up from there. I have tried this twice and both discs started burning, but ended in an error roughly 10 minutes later stating "The attempt to burn a disc failed. The device failed to respond properly, unable to recover or retry." I have tried two separate brands of discs, one being a brand new spool. I had some trouble with my MacBook Pro not burning DL DVD's last month and I took it to see a genius, and of course it worked in the store. Any help please?