Some Mac owners are being prevented from installing OS X Lion, talk on Apple's support forums shows. In select instances users will pick a destination drive and be given an error message, such as "this disk cannot be used to start up your computer," or "this disk is used for Time Machine backups," even though the target was previously used to boot up Snow Leopard. The issue can happen regardless of how much space is on the drive, and whether or not a Mac meets other Lion system requirements.
