I can't erase a DVD-RW. It's not that old, but has a few scratches on it. I burned it with iDVD, but now want to erase it. Both Disk Utility and Toast fail. DU just greys out the erase. Toast tries, but says that another resource has the disk. This is just after inserting it (with no auto-play). Any guesses? And yes, I am certain that it's a RW!