using early 2008 era iMac. Using Final Cut Express to edit. Then I burn to disk using IDVD. Just burned a disk using a memorex dvd-r 16x 4.7gb 120 min disk. It burned normal. Then it asked me to burn another and I used a brand new pack of Sony dvd-r 120 min 4.7gb 16x/1x disks. When I put it in it sits for a second and kicks it out telling me to insert a recordable disk. I tried about half the package and none work. I thought they were the same. Ideas?!