I used my older MBP running 10.7.4 to repartition an external hard drive that I want to use for backups. No problem after repartition and it shows in Finder. Switch to newer MBP running 10.8.1. It can't mount the external hard drive. I've tried repairing and repartitioning in 10.8.1. Can't do either because the OS can't mount the drive. Any suggestion as to what I need to do to get this drive acknowledged by ML?