I'm trying to insert these DVD+RWs from Sony into my iMac (20" Late 2006), and after spinning them a few times, the optical drive spits 'em back out. According to Mactracker.app, the specs for this iMac state "Slot-loading SuperDrive w/ 2.4x Dual Layer burn (DVD+R DL/DVD±RW/CD-RW" -- so what am I missing?